N.B.: Only in the present subchapter the terms are given as used by the cited authors. In all other parts we apply a uniform terminology.

“For more than half a century uredinology has suffered from a deficiency, that is the lack of a generally accepted terminology” of the spore states and life cycles (Holm 1984: 221). This situation still persists. The “old European terminology” (l.c. 222) was mainly based on terms already used by De Bary (e.g., 1865, 1866): spermogonia, aecidia, uredosori, teleutosori. De Bary’s definition of these spore states is based on both, their position in the life cycles and their morphology. Arthur (1905) introduced a new set of convenient, short terms for the spore states, excluding ambiguous terms identical with generic names like Aecidium, Caeoma, Peridermium and Uredo: spermogonium was replaced with pycnium, aecidium/caeoma/peridermium with aecium, uredo/uredosorus with uredinium (later ‘uredium’), teleutosorus with telium. Arthur et al. (1907–1924) used these new terms in the ‘North American Flora’. Although Arthur united some morphologically different types of sori under the term ‘aecium’ there, the definition of this spore state was still based on both, the position in the life cycle and the morphology of the respective type of aecium.

Subsequently Arthur wanted to go further, i.e. to establish “terms for the positions in the life cycle that did not have a specific morphologic connotation” (Hennen and Hennen 2000: 123). In the course of these efforts, Arthur (1925, 1932) gave his terms new meanings correlated with the alternation of generations: “Arthur (1925) accepted the concept that spermogonia and aecia are structures produced on the thallus (body) of the gametophyte generation, [and] that aeciospores initiate a new thallus (body) which represents the sporophyte generation” of plants from the algae, mosses, liverworts, and through all of the groups of vascular plants (Hennen and Hennen 2000: 118–119). In the ‘Manual of the Rusts in United States and Canada’ Arthur (1934) finally abandoned all ‘morphological connotations’ he had accepted earlier in the ‘North American Flora’. Aeciospores were defined as “non-repeating spores produced as a result of dikaryotisation”, urediospores as “repeating vegetative spores produced on a dikaryotic mycelium” (Cummins and Hiratsuka 1983: 2).

These new definitions led to new morphological descriptive terms which were adopted by many American and rejected by most European authors (e.g., Guyot 1938, 1951, 1957; Gäumann 1959; Majewski 1977, 1979) who followed the terminology of De Bary. For instance, ‘uredoid aecia’ sensu Arthur means that these aecia ‘resemble’ uredinia (morphologically they are uredinia and usually associated with spermatogonia); ‘aecioid uredinia’ sensu Arthur means that these uredinia ‘resemble’ aecia (morphologically they are aecia but not associated with spermatogonia). “The only ‘morphology’ in Arthur’s new system was the nuclear condition of the initiating mycelium: monokaryotic for aecia and dikaryotic for uredinia and telia” (Savile 1988: 387). Such an ‘ontogenic’ terminology forces us to use different terms for obviously homologous structures.

In the ‘Illustrated Genera of Rust Fungi’ Cummins (1959) adopted the ‘ontogenic’ terminology introduced by Arthur (1925, 1932) and implemented in ‘The Plant Rusts’ (Arthur et al. 1929) and in the ‘Manual of the Rusts in United States and Canada’(Arthur 1934). Since then, the terminology of spore states and life cycles of rust fungi has been discussed controversially by several authors, e.g., Gäumann (1964), Laundon (1967, 1972, 1973), Savile (1968, 1979, 1988), Hiratsuka (1973b, 1975), Holm (1973, 1984, 1987), Durrieu (1979), Cummins and Hiratsuka (1983, 2003), Poelt and Zwetko (1997), and Hennen and Hennen (2000). Moreover, some authors of European rust florae were not quite aware of the pitfalls and mixed terms from De Bary’s and Arthur’s terminology.

In agreement with Savile (1979) we follow De Bary’s concept but adopt the following convenient terms for the spore states introduced by Arthur (1905) and used in the ‘North American Flora’ (Arthur et al. 1907–1924): aecium (incl. aecidium, caeoma, peridermium), uredinium, and telium. The same terminology is applied in the present standard identification handbook by Klenke and Scholler (2015).

Jørstad (1964a: 28) noted, that in his “text ‘aecidia’ is often used as a common term for aecidia and caeomata”. His foot-note shows that the old European terminology is somewhat problematic. Uredinologists used to treat the names of anamorph taxa as synonyms, as soon as the whole life cycle of a rust fungus has been detected, and referred to the name of the teleomorph as species name. This practice lasts for more than hundred years. In Gäumann’s (1959) discussions, the terms ‘die Uredo’, ‘die Aecidien’, ‘die Caeomata’ referred to spore states without saying. However, the mixing of generic names like Aecidium, Caeoma and Uredo with names of spore states causes problems and confusion. The name Uredo had been used for the uredinial state of the whole rust fungi by many authors for a long time. According to Cummins and Hiratsuka (2003) genera like Melampsora, Ochropsora, Puccinia, Tranzschelia and Uromyces have uredinia of Uredo-type. When including the anamorphs of all these genera, Uredo represents a spore state but not a taxon. Nevertheless, the definition given by Cummins and Hiratsuka (2003) for the anamorph genus Uredo is much narrower than it is traditionally. Besides Uredo, several other anamorph genera apply to the uredinial states of rust fungi, e.g., Calidion, Malupa, Milesia, and Uredostilbe. The genus Calidion “was established to accommodate the uredinial state of a rust on a fern” (Cummins and Hiratsuka 2003: 37), but also the genus Phragmidium (a rust on Rosaceae) has uredinia of the Calidion-type. So far, the way of treating anamorphic genera by uredinologists is unsatisfactory. Therefore, a term or name should not be used for both, taxon and spore state. Arthur (1905) has already developed such a terminology of spore states which is applied here in the sense of Savile (1979, see above). For a basic overview of the terms for rust sori and spores see also Table 2 (p. 171).

0: Spermatogonium (‘spermogonium’, pycnium)

This organ produces spermatia (pycniospores) and nectar, which attracts insects. Production of spermatogonia is one of the most spectacular phenomena in the world of phytoparasitic fungi. Many rusts induce formation of pseudoflowers (Fig. 4) that resemble true flowers in colour and shape (Pfunder and Roy 2000). Usually, spermatogonia are produced on bright yellow, reddish or purple-red leaf spots and swellings, often also on deformed petioles and stems in crowded groups of various size. Like true flowers, fungal pseudoflowers present a sweet-smelling nectar, which contains spermatia that are transferred by nectar-feeding insects (Pfunder et al. 2001). They are thus analogous to the entomophilous perfect flowers.

I: Aecium (aecidium, caeoma, peridermium, etc.)

This sorus bears aeciospores. Usually, these are the first dikaryotic spores in the life cycle. In many rust fungi, they initiate the alternation to another host. Aeciospores are catenulate, i.e., they are produced in chains. Usually, their walls are described as verrucose, but in many instances, however, the understanding of morphological criteria in aeciospore ornamentation is inadequate (Savile 1973; Zwetko and Blanz 2012, 2018).

Aecia are produced on leaves, branches, stems and cones where the fungus often causes bright yellow, reddish or purple-red discolouration and deformation of the surrounding host tissue. In addition, the spores in the aecia are usually bright orange by carotenes and are, therefore, easily visible. But in some genera (e.g., Milesina and Uredinopsis) and in some Puccinia and Uromyces species (e.g., P. phragmitis and U. appendiculatus) the spores are hyaline.

According to their gross morphology, the following main types of aecia are distinguished (these terms are derived from the genera Aecidium, Caeoma, Peridermium and Roestelia):

1. Aecidioid aecia are usually cup-shaped with aeciospores borne within the whitish, cylindric peridium. When mature, their well-developed peridium is regularly opening at the roundish apex, and the revolute margin of the peridium is ± divided into several irregular lobes, which are usually not tapering towards the top. The peridial cells are ± rhomboidal. This type of aecia is characteristic for the Puccinia-Uromyces complex and can be found on numerous angiosperms except Poaceae, and (at least in Europe) Juncaceae and Cyperaceae. Usually, aecidioid aecia occur soon after the spermatogonia in spring.

Aeciospores of the Puccinia-Uromyces complex (Fig. 5) have characteristic patterns of wall ornamentation. In species on several members of Ranunculaceae and Asteraceae, the apical spore region has been found to exhibit conspicuous features, either a smooth, round cap or a hole, surrounded by an annulus (Zwetko and Blanz 2012). These features are hardly recognisable in a light microscope, and have, therefore, not been described before. However, these features help to recognise apex and basis of isolated aeciospores. When knowing the position of the apex, the regular sequence of spore surface zonation from the apex to the base is evident. It consists of a small, circular, finely verrucose apical zone, surrounded by a broad belt with coarse warts or with coarse warts and dehiscent platelets, respectively. These large platelets have been termed ‘abfallende Plättchen’ by Klebahn (1914), ‘refractive granules’ by Holm (1967), or ‘pore plugs’ by Savile (1973). Shape and size of these platelets provide valuable taxonomic characters (see Holm 1967; Savile 1973; Zwetko 1993). The surface of the basal hemisphere is finely verrucose as it is at the apex. Therefore, the spore surface is not bizonate – as supposed by Savile (1973) – but trizonate.

1. Aecidioid aecia of the Ranunculaceae-Rosaceae rusts Ochropsora (Ochropsoraceae), Tranzschelia and Leucotelium (Tranzscheliaceae) differ from those of the Puccinia-Uromyces complex by their broad revolute peridium, which is divided into a few broad lobes; the lobes are tapering towards the top. The aecia arise from a systemic mycelium, which can persist for years. They cover the lower surface of the leaves ± completely. Infected leaves are paler, the stems are longer, and affected plants usually do not flower. The spores of this type of aecia exhibit an uncommon character. Their walls are pigmented, and their contents lack carotenes. Already Sydow and Sydow (1904) emphasised that the aeciospores of Puccinia mostly have a hyaline wall, and the orange-yellow or orange-reddish colour of their spore contents is due to the presence of carotenoid-rich lipid droplets (Zwetko and Pfeifhofer 1991).
2. Caeomoid aecia in the stricter sense mainly occur in the genus Melampsora and lack peridia, but some Melampsora species have peridial cells adherent to the epidermis of the host plant. In Mikronegeria a single layer of overlying thin-walled cells exists; this layer has little resemblance to a peridium, and breaks up with the overlying host epidermis (Peterson and Oehrens 1978). Melampsora and Mikronegeria produce aecia on conifers, the former also on some angiosperms.
3. Caeomoid aecia on Rosaceae are produced by Phragmidium and other Phragmidiaceae. In analogy to paragraphs 1, 3, 5 and 6, this type of aecia could better be named lecytheoid aecia, after the anamorph taxon Lecythea Lév. The aecia on this host family and the ornamentation of their aeciospores distinctly differ from those of Melampsora and Mikronegeria, they represent a separate type of aecia. Aecia of Phragmidium are surrounded by clavate paraphyses. Aecia of Melampsora and Mikronegeria lack paraphyses.

Sometimes, it is difficult to distinguish aecio- and urediniospores in this family. The aecio- und urediniospores of Phragmidium fragariae, for instance, show the same ornamentation of the spore wall in SEM, i.e. plateau-shaped warts, with small spines on the plateau. Such warts are also known from aeciospores of other Phragmidium species, e.g., Ph. tuberculatum (Bedlan 1984; Wahyuno et al. 2002). Thus, the urediniospores of Ph. fragariae might be secondary aeciospores. On the other hand, there are also Phragmidium species with echinulate aeciospores which are very similar to urediniospores, e.g., Ph. mucronatum (l.c.). – The aeciospores of the genus Trachyspora are interpreted by several authors as urediniospores or ‘uredinioid aecidiospores’ (e.g., Gäumann 1959; Wilson and Henderson 1966; Gjærum 1974; Helfer 2005; Klenke and Scholler 2015). Henderson (1973) studied the ultrastructure and development of these spores, and the ontogeny of the spine-like surface sculpture confirmed that they are aeciospores.

1. Peridermioid aecia are cylindrical, tongue-, sac- or blister-shaped. The peridium consists of relatively long and narrow, thick-walled cells arranged in one or several layers. It is irregularly fragmented at maturity. Such aecia are characteristic of the families Coleosporiaceae (incl. Cronartiaceae), Milesinaceae, and Pucciniastraceae. Within the rust fungi, this type of aecia represents a unique character, and its exclusive occurrence on conifers (Pinaceae) leads to special adaptations of the parasites to their host plants. Peridermioid aecia often occur late in summer or in autumn. In Milesina, the aecia are found about two or three months after the spermatogonia on needles of the current season. In Hyalopsora, the spermatogonia occur on needles of the previous season and the aecia on needles of the second previous season.

Spores in peridermioid aecia represent a unique character, too. They are often characterised by a smooth or nearly smooth strip from the apex to the base on one side of the spore. SEM images show these regularly arranged strips as longitudinal overlying structures or as areas with distinctly finer warts. The former have been observed in the genera Chrysomyxa, Cronartium or Pucciniastrum, the latter in the genera Milesina and Uredinopsis (see Zwetko and Blanz 2018).

1. Roestelioid aecia are usually cornute-shaped. At first, their peridia are cylindrical and closed at the apex. At maturity, they generally tend to rip longitudinally. The time of maturity is uncommon. In spring (May or June) large, reddish spots with spermatogonia occur on the upper side of the leaves. These leaf spots increase and swell till the end of summer (August or September); then aecia are produced on the lower side of the leaf spots. The aeciospores exhibit an uncommon character, as well. Their walls are usually pigmented, with distinct scattered germ pores. The ultrastructure of the aeciospore surface has been analysed in detail by Lee and Kakishima (1999). The roestelioid aecium is characteristic of the genus Gymnosporangium and its anamorph Roestelia. It is produced on Rosaceae (‘Maloideae’).

According to their position in the life cycle, the following types of aecia are distinguished:

I: Aecia of endo-forms produce aeciospores which serve as probasidia and germinate with basidia at maturity.

Ia: Primary aecia are produced in association with spermatogonia.

Ib: Secondary aecia are repeating aecia, not in association with spermatogonia. Mostly, these kinds of aecia are produced by autoecious rusts, but in the genera Chrysomyxa and Coleosporium they replace the uredinia on the alternate host. Because of host alternation, most authors (even Gäumann 1959) defined these secondary aecia as uredinia, although their spores are formed in chains. According to their morphology, the secondary aecia of Chrysomyxa are peridermioid and those of Coleosporium caeomoid.

II: Uredinium (uredosorus, ‘uredium’)

In the evolution of rust fungi, the morphology of uredinia is less variable than that of aecia and telia, and the genus name ‘Uredo’ has been used for the uredinial state of all rust fungi by many authors for a long time. Usually, this sorus is produced by a dikaryotic but sometimes also by a monokaryotic mycelium (primary uredinia). It bears urediniospores, which are one-celled and borne singly on pedicels; generally their walls are echinulate. The hilum, a scar on the spore at the point of attachment to the pedicel, is usually easily visible and distinguishes urediniospores from aeciospores. Uredinia occur on leaves, stems, fruits or fronds where the fungus often causes small yellow spots. Savile (1968) showed that Arthur’s term ‘uredium’ is incorrect.

According to their gross morphology, the following main types of uredinia are distinguished:

1. Uredinioid uredinia are usually subepidermal in origin, and erumpent, releasing a more or less pulverulent spore mass. This type of uredinia occurs in several groups of rust fungi, which are not closely related. Therefore, the following subdivision is somewhat tentative and perhaps of limited suitability:

• Uredinoid uredinia of the genus Melampsora are characterised by spores with unpigmented walls, bright orange-reddish contents and intermixed, persistent paraphyses also with unpigmented walls. Germ pores are difficult to observe. The peridium is soon evanescent, and the paraphyses are uniformly distributed throughout the sori.
• Uredinioid uredinia of the Puccinia-Uromyces complex bear spores with mostly pigmented walls, but the degree of pigmentation varies widely. In Puccinia coronata, for instance, the walls are nearly hyaline. Usually, the germ pores are visible in LM. The majority of Puccinia and Uromyces species lack paraphyses; in Europe only some graminicolous species like P. arrhenatheri, P. brachypodii, P. deschampsiae and P. poae-nemoralis possess persistent paraphyses. The paraphyses of P. coronata and P. striiformis collapse readily and are easily overlooked.
• Uredinioid uredinia of the Sonchus rust Puccinia pseudosphaeria (syn. Peristemma P., Miyagia P.). In analogy to the terms applied for aecia, this type of uredinia could be named ‘peristemmoid’ uredinia.
• Uredinioid uredinia of the Rosaceae rust genus Phragmidium are usually surrounded by paraphyses, but a peridium is lacking. Cummins and Hiratsuka (2003) called such uredinia the ‘ Uredostilbe-type’.

1. Milesioid uredinia possess a delicate peridium, which is hemispherical or flat and opens by a regular or irregular pore, with or without distinct ostiolar cells. We have chosen this term in analogy to the terminology of aecia; Cummins and Hiratsuka (2003) called it ‘ Milesia-type’. The pedicels of the urediniospores are often short and inconspicuous. Milesioid uredinia are typical of various genera of the Melampsorineae (except Melampsora, see above), e.g., Thekopsora, Milesina, Melampsoridium and Pucciniastrum.

According to their position in the life cycle, the following types of uredinia are distinguished:

IIa: Primary uredinia are produced in association with spermatogonia and replace the aecia.

IIb: Secondary uredinia are produced subsequently and independent from spermatogonia.

According to its position in the life cycle and and its different morphology, the following third type of uredinia is distinguished:

II*: Amphisporic sori (amphisori, amphioid uredinia) bear amphispores. The fern rust genera Uredinopsis and Hyalopsora and some Puccinia species on Carex have urediniospores of two kinds: thin-walled spores immediately germinating for propagation in summer, and so-called amphispores, urediniospores of the second kind, which have thicker walls and probably undergo a resting condition before germination. They are produced later for persistence. Spores intermediate between urediniospores and amphispores occur in some sori of, e.g., Hyalopsora aspidiotus. Amphispores differ from normal urediniospores also by their wall ornamentation.

III: Telium (teleutosorus)

Usually, this sorus is produced by a dikaryotic, but sometimes also by a monokaryotic mycelium (microcyclic rusts with spermatogonia). It bears teliospores. In temperate, alpine and arctic climates teliospores are mostly resting spores, which are capable of germination only after a period of winter dormancy. But in some genera (e.g., Kuehneola, Leucotelium, Cronartium, Melampsorella) and some species (e.g., Phragmidium duchesneae, Puccinia arenariae, P. chrysosplenii, P. malvacearum) germination occurs without dormancy. Puccinia salviae and some Puccinia species on the genus Veronica s.l. (like P. albulensis, P. paederotae, P. veronicae-longifoliae, and P. veronicarum) produce both kinds of teliospores, resting and non-resting spores. Such non-resting teliospores are also named ‘leptospores’ (but this term is often restricted to ‘lepto-forms’ – see below).

In most genera of rust fungi teliospores are arranged in sori, but in the genera Uredinopsis, Milesina and Hyalopsora, we find single, variably shaped spores or spore balls scattered in the mesophyll tissue or spores – uni- or multicellular by vertical septa – formed within the epidermis cells, but no well-organised sori. In Melampsoridium and Melampsora, the spores are grouped into a tight palisade or crust below the epidermis or the cuticula. The telium of the genus Cronartium consists of an erumpent long column of strongly adherent spores. “Increased exposure of the teliospores has evidently proved advantageous whenever it has occurred, for there is a steady trend in this direction, ... in several distinct evolutionary lines” (Savile 1955a: 87). All these genera have non-pedicellate teliospores. “Perhaps the greatest single advance in teliospore evolution was the initiation of spore pedicels. ... The pedicel may have developed in some lineages by specialisation of a cell of the mycelium on which the spore was borne. I suspect, however, that it generally developed ... by a transfer of the mechanism used in the uredinium: a meristematic basal cell cuts off a series of spore mother-cells, each of which divides into spore and pedicel” (Savile 1976: 158).

In the phylogeny of rust fungi, the morphology of aecio- and urediniospores remains rather constant, but the teliospores vary greatly in morphology. Therefore, the two anamorph states are easily distinguishable by morphological characters. Holm (1987: 434) agreed to the definition of teliospores by Hiratsuka (1973b): “The only workable definition of a teliospore is that it will form basidia upon germination”.

According to their position in the life cycle, the following types of telia are distinguished:

IIIa: Primary telia are often produced in association with aecia or primary uredinia, respectively.

IIIb: Secondary telia are not associated with aecia or primary uredinia.

III*: Basidiosori are interpreted in two different ways. Either as telia consisting of teliospores forming an ‘internal basidium’ at maturity (recognisable by insertion of three septa), or simply as sori consisting of basidia. We prefer the second interpretation. The most common examples are found in the genus Coleosporium, where the basidiosori appear as small, often red, wax-like crusts; except for their apex, the basidia of Coleosporium are thin-walled (Fig. 13, p. 194).

IV: Basidium (metabasidium)

Basidia and basidiospores are hardly ever described in detail, presumably rather uniform and of little diagnostic value. The basidium is normally a four-celled, transversely three-septate, straight or curved (meta-)basidium. Each cell develops a sterigma with a thin tip where the basidiospore is formed and finally released as a ballistospore with the help of Buller’s drop (e.g., Webster and Weber 2007), but there may be more exceptions than hitherto observed. Germination of basidia in basidiosori (see above) is somewhat divergent; in Coleosporium, each of the four cells of a basidium produces a long sterigma-like tube which breaks through the surface and forms a ballistospore at the tip.

Based on the reduction of spore states, five main types of life cycles have been distinguished by European authors:

0, I, II, III, IV Eu-form

• Auteu-form, not host alternating
• Hetereu-form, host alternating; Jørstad (1964a) distinguished

• obligate host alternating forms
• facultative host alternating forms

0, I, III, IV Opsis-form (reduction of uredinia)

• Autopsis-form, not host alternating
• Heteropsis-form, host alternating

0, II, III, IV Brachy-form (reduction of aecia)

II, III, [IV?] Hemi-form (whole monokaryotic stage absent); this form is considered to be a hetereu-form originally, but alternation no longer takes place. Some rusts are known as hetereu-form, but in some areas alternation does not occur, and the telial stage is often suppressed. For other rusts considered as hemi-forms host alternation is not known at all.

(0), III, IV Micro-form (reduction of aecia and uredinia; forms with spermatogonia are rare)

• Typical micro-form with resting teliospores
• Lepto-form, with non-resting teliospores (leptospores; spore walls usually thinner and brighter than in resting teliospores)

Sometimes a sixth main type has been defined:

0, I, IV Endo-form; its aeciospores produce basidia and basidiospores upon germination.

Several variations and modifications of these main types exist in nature. Separate names for such variations are not helpful and would rather cause unnecessary complications. We have already used the Roman numerals like formulas (see above). With these symbols we can describe the life cycle of each rust species in detail, for instance:

(0, I), II, II*, III, IV cycle of Uredinopsis struthiopteridis

0, I, [II], III, IV cycle of Puccinia firma

I, II, III, IV cycle of Puccinia karelica

I, [II], III, IV cycle of Puccinia rupestris

0, I, II, IV cycle of Ochropsora anemones

0, Ia, Ib, III, IV cycle of Chrysomyxa rhododendri

0, Ia, Ib, IV cycle of Coleosporium tussilaginis

(0?), Ia, IIIa, Ib, IIIb, IV cycle of Puccinia senecionis

0, IIa, IIIa, IIb, IIIb, IV cycle of Puccinia punctiformis

Ia, IIIa, [Ib], IIIb, IV cycle of Trachyspora alchemillae

[Ia], IIIa, IV cycle of Trachyspora alchemillae in N Europe and at higher altitudes

0, IIa, IIb, IIIb, IV cycle of Triphragmium ulmariae

0, IIa, IIIa, IV cycle of Triphragmium ulmariae at higher altitudes

In our descriptions of rust taxa, the Roman numerals and the names of the host plants are listed together. This arrangement shows at once whether a life cycle is obligatorily heteroecious (e.g., Puccinia firma), facultatively heteroecious (e.g., Uredinopsis struthiopteridis), or autoecious (e.g., Puccinia senecionis, P. punctiformis):

Puccinia firma

0, I on: Bellidiastrum michelii

[II], III, IV on: Carex firma

Uredinopsis struthiopteridis

(0, I on: Abies alba, A. balsamea)

II, II*, III, IV on: Matteuccia struthiopteris

Puccinia senecionis

(0?), Ia, IIIa, Ib, IIIb, IV on: Senecio nemorensis agg.

Puccinia punctiformis

0, IIa, IIIa, IIb, IIIb, IV on: Cirsium arvense

auct. [sensu] auctorum [aliorum], in the sense of other authors (not according to the original description and/or the type material)

diam. diameter

f.sp. forma specialis, special form (an infraspecific category not covered by the ICN)

l.c. loco citato, in the source cited immediately above

N.B. nota bene (note well, note especially)

p.p. pro parte, in part

s. … sensu, in the sense of …

s.l. sensu lato, in a broad sense

s. latiss. sensu latissimo, in the widest sense

s.str. sensu stricto, in a narrow sense

s. strictiss. sensu strictissimo, in the narrowest sense

spp. some or all species (of a genus)

A few acronyms of public herbaria from Index Herbariorum (Thiers 2024) are used.

Key to the rusts on cone scales of Picea (p. 207)

Key to the Melampsora species on Salix (p. 214)

Key to rusts on Euphorbia (p. 228)

Key to the Melampsora species on Salix caprea when only uredinia are present (p. 233)

Key to the Melampsora species on Populus (p. 238)

Key to the Melampsora species on Salix viminalis (p. 243)

Key to the Melampsora species on Salix retusa (p. 245)

Key to the rusts on needles of Abies (p. 250)

Key to the Melampsoridium species in Europe (p. 263)

Key to the Gymnosporangium species on Juniperus in Central Europe (p. 273)

Key to Gymnosporangium species in the aecial stage (p. 274)

Key to the Phragmidium species on Rosa (p. 294)

Key to the rusts on Rubus in the aecial and uredinial stage (p. 305)

Key to the rusts on Rubus in the telial stage (p. 305)

Key to the Trachyspora species in Europe (p. 306)

Key to the rusts on Prunus in Europe (p. 312)

Key to the Tranzschelia species in Central Europe (p. 312)

In the present treatment, we adopt a narrower family concept supported by recent phylogenetic studies, mainly from Aime et al. (2018a) and Aime and McTaggart (2020).

The Pucciniales (formerly Uredinales) have been divided into only two families by Dietel (1928), Melampsoraceae and Pucciniaceae, a concept which was accepted by other authors for a long time. The Pucciniaceae usually have pedicellate teliospores, whilst the teliospores of Dietel’s Melampsoraceae are non-pedicellate but otherwise rather variable including hardly detectable simple spores inside the mesophyll or inside the epidermis cells, as well as spores arranged in conspicuous flat crusts, chains or columns.

Based on aecia, uredinia, telia and host ranges, Dietel (1928) distinguished the five tribes Pucciniastreae, Cronartieae, Chrysomyxeae, Coleosporieae and Melampsoreae within the Melampsoraceae. Gäumann (1959) treated Dietel’s five tribes as families. With the exception of the Pucciniastraceae, they were represented in Central Europe only by their type genera.

Hiratsuka and Cummins (1963) emphasised the importance of spermatogonia and recognised eleven morphological types. Based on these types, Cummins and Hiratsuka (1983, 2003) accepted 13 families worldwide, including Coleosporiaceae, Cronartiaceae, Melampsoraceae and Pucciniastraceae, but united Chrysomyxaceae with Coleosporiaceae. Aime (2006) expanded the Coleosporiaceae once more, incorporating also Cronartiaceae and Pucciniastraceae. Until now, neither the monophyly of the Pucciniastraceae nor of the Coleosporiaceae is well-supported by molecular data (Maier et al. 2003; Aime 2006; Aime and McTaggart 2020) and ultrastructure (Berndt 1993, 1996; Berndt and Oberwinkler 1995, 1997). Only the Melampsoraceae s.str. proved to be monophyletic and separate from the other families by a long genetic distance (Maier et al. 2003). Pei et al. (2005a, b) clearly demonstrated the close relation between the Melampsora species on the one hand and the comparatively loose connection with the other genera in this chapter, a finding confirmed by Aime (2006). In their study on Chrysomyxa, Feau et al. (2011) also showed that this genus is clearly distant from Melampsora.

Aecia are the most diverse sori of the Melampsorineae. Melampsoraceae s.str. are characterised by (often quite delicate) caeomoid aecia without a distinct peridium. In contrast, all other families (Coleosporiaceae, Milesinaceae, Pucciniastraceae) produce peridermioid aecia. Within the rust fungi, this type of aecia represents a unique character, and the fact that this type exclusively occurs on conifers gives evidence of the coevolution of host and parasite.

Peridermoid aecia are cylindrical, tongue- or blister-shaped, and the blister is often flattened in one plane. The peridium consists of relatively long and narrow, thick-walled cells arranged in one or several layers. It irregularly ruptures at maturity. In peridermioid aecia, the peridium forms by the differentiation of the distal-most cells of the aeciospore chain into the thick-walled peridial cells (Colley 1918; Littlefield and Heath 1979). This contrasts clearly with the mode of peridium morphogenesis in aecidioid aecia (Puccinia-Uromyces complex) where peripheral chains of aeciospores and intercalary cells differentiate to form the tubular peridium around the elongated aecia (Fromme 1914; Littlefield and Heath 1979). The lateral wall of the aecial peridium in Puccinia and Uromyces originates from aeciospore mother cells. But at least in some Melampsorineae its cells are the equivalents of aeciospores, and small residual intercalary cells may be encountered. This lateral wall is a structure that arose ‘de novo’ in the aecium under the necessity for a powerful thrust being exerted upon the epidermis (Savile 1955a). This author presented an interpretation for the different mode of peridium morphogenesis in peridermioid and aecidioid aecia: It is not certain that the original gymnospermous hosts had as tough an epidermis or cuticle as Abies, on which the contemporary fern rusts produce their aecia; but the very robust peridia of peridermioid aecia of most genera of the Melampsorineae show us the morphological adaption that was necessary. In the majority of angiospermous hosts rupture of the epidermis presents no great problem. In the Puccinia-Uromyces complex the principal function of the peridium is to maintain the pressure needed for forcible discharge of the aeciospores.

Zwetko and Blanz (2018) showed that the mechanical problem of rupture of the epidermis on gymnospermous hosts characterises not only the morphology and morphogenesis of the aecial peridium but also the morphology of the aeciospores. Zwetko and Blanz (2018) compared spores in aecidioid aecia with spores in peridermioid aecia. In aeciospores of aecidioid aecia of the Puccinia-Uromyces complex, the aeciospore wall is distinctly trizonate in certain species, with a circular, almost smooth, only finely verrucose apical cap, a broad lateral belt with more or less coarse warts (sometimes with dehiscent pore plugs), and a finely verrucose basal hemisphere (Zwetko and Blanz 2012). In contrast, aeciospores from peridermioid aecia show a peculiar longitudinal structure, i.e., a broad smooth strip from the apex to the base of the spore. Klebahn’s (1914) excellent drawings already show such a smooth strip on aeciospores in the genera Cronartium, Melampsoridium and Pucciniastrum s.l., and his observations were confirmed by several other authors who studied one or more genera (e.g., Peterson 1967; Hiratsuka 1971; Kaneko 1981; Hiratsuka and Sato 1982; Sato and Sato 1982; Crane 2001). In a study on Chrysomyxa, Crane (2001) was apparently the first who described the longitudinal structure as an occasionally groove-like overlay on one side of the aeciospore connecting two narrow, irregular caps. Zwetko and Blanz (2018) confirmed this finding in their SEM studies of aeciospores of Thekopsora areolata, Chrysomyxa rhododendri and Cronartium flaccidum. Moreover, they stated that the broad longitudinal strip with distinctly finer warts on the aeciospores of Milesina and Uredinopsis can be interpreted as a homologous structure.

Such smooth longitudinal structures are absent on the aeciospore walls of other rust genera. For instance, Littlefield and Heath (1979) described and illustrated the ultrastructure of the aeciospore wall and its development in Melampsora lini and Puccinia recondita. In immature aeciospores of Melampsora lini (s.l.) a mucilage-like interstitial matrix between warts appears to condense or to break down, exposing evenly spaced ornaments (warts) over the whole surface of the spore. A similar process occurs in Puccinia recondita, although the interstitial matrix lacks the mucilage-like appearance of that in M. lini. SEM photos of young aeciospores of P. recondita in Littlefield and Heath (1979) show an irregular and variable interstitial matrix (primary spore wall) covering the wall ornaments. The interstitial matrix disappears at an early stage, and the ornaments of mature P. recondita aeciospores are fully exposed. The smooth, more or less circular apical cap of the aeciospore wall (which is typical of many taxa in the Puccinia-Uromyces complex) does not disappear at maturity (Zwetko and Blanz 2012).

Another distinct feature of the aeciospore wall of Coleosporiaceae, Milesinaceae and Pucciniastraceae is the ‘annulate’ structure of the wall ornaments (warts) proper which are built of two to several stacked discs, sometimes tapering towards the top; moreover, these stacks are longitudinally furrowed in some taxa. Zwetko and Blanz (2018) figured a remarkable ‘gradation’ among the wall ornaments of Melampsorineae on conifers: In Chrysomyxa rhododendri (and many others) the ornaments of the (primary) aeciospores consist of several stacked disks, in Rossmanomyces pyrolae they are built of two cushion-like discs on a stout base, and in Melampsora laricis-epitea they consist of only two elements, a stout base and one globose structure on top (Figs 8d, 19b, 23 on pages 186, 204, 208).

In the evolution of rust fungi, the morphology of uredinia is less variable than that of aecia and telia. Urediniospores are borne singly on pedicels and mostly echinulate. The uredinia of several genera within the Melampsorineae are covered by a hemispherical or flat peridium, opening by a regular or irregular pore with or without clearly differentiated ostiolar cells. In Melampsora, the peridium is soon evanescent, and the sori possess abundant, persistent paraphyses, which are uniformly distributed throughout the sori. The spore walls in Melampsora are hyaline, and the germ pores are usually invisible. Special methods of preparation are needed to study the pores (see Kaneko and Hiratsuka 1982).

For the morphological characters of telia, see the various families and genera of the Melampsorineae.

Recent circumscriptions of the Coleosporiaceae are provided by Hardtke et al. (2021) and Aime and McTaggart (2020). Currently the family comprises some genera of conifer rusts previously separated in different families by morphological characters and host range, especially Chrysomyxaceae and Cronartiaceae (e.g., Gäumann 1959). Inclusion of Cronartiaceae was suggested by Aime (2006), transfer of Thekopsora from Pucciniastraceae by Aime et al. (2018a). Consequently, this family is very diverse from the morphological point of view but also in the host ranges of the genera. The ‘uredinia’ of Chrysomyxa, Rossmanomyces and Coleosporium formed on the telial hosts after alternation are actually secondary aecia, recognizable by secondary aeciospores which are produced in chains. Telia are rather diverse, teliospores mostly not dormant. The ‘telia’ of Coleosporium, however, are basidiosori, and their ‘teliospores’ are regarded as basidia here. Most species are heteroecious and macrocyclic, with some derived microcyclic or probably endocyclic species. Uredinia/secondary aecia and telia/basidiosori of Coleosporiaceae are found on plants of various families of dicotyledons.

The small genus occurs in the N temperate region (Europe, Asia and N America). It is usually host alternating (except for derived species like the micro-form Ch. abietis) and produces spermatogonia and primary aecia on Picea, and secondary aecia and telia on Ericaceae s.l. (incl. Empetraceae). Because of host alternation, most authors (e.g., Gäumann 1959; Klenke and Scholler 2015) defined the secondary aecia as uredinia, and we add this alternative interpretation in parentheses. Radial sections through the lateral part of secondary aecia of Chrysomyxa empetri and Ch. rhododendri show that the development of spores and peridium starts from short chains of cells of which the apical cells transform into peridial cells (Berndt 1999b). This type of spore and peridium formation characterises peridermioid aecia. – Spermatogonia amphigenous on needles, subepidermal (Group I, type 2, according to Cummins and Hiratsuka 2003). – Primary aecia peridermioid, subepidermal in origin, erumpent; peridium well-developed, membranous, consisting of a single layer of cells and dehiscing irregularly at the apex. – Primary aeciospores catenulate with intercalary cells; wall hyaline, coarsely warted, often with a longitudinal, smooth strip; warts (ornaments) annulate. – Secondary aecia (uredinia) peridermioid, subepidermal, erumpent, pulverulent, with or without a very delicate peridium. – Secondary aeciospores (urediniospores) catenulate, formed in basipetal succession together with intercalary cells, resembling primary aeciospores. – Telia subepidermal in origin, erumpent, pulvinate, waxy. – Teliospores in simple or branching chains, 1-celled, with thin, hyaline walls, not separated by intercalary cells, germinating without dormancy. – Basidia are formed by elongation of the apex of uppermost teliospores or between the loose and mostly collapsed outermost spores.

Dietel (1928) suggested that Chrysomyxa is related to Thekopsora because both genera occur on Ericaceae. Gäumann (1959) defined two ‘form groups’ (Formen­kreise) within the genus, based on host range and infestation behaviour. The first group (Ch. rhododendri group) includes species with (±) localised haplophase mycelium on spruce needles and dikaryotic phase on Ericaceae: Ch. empetri, Ch. ledi, Ch. rhododendri, and the micro-form Ch. abietis. The second (Ch. pirolatum group), has recently been separated as the genus Rossmanomyces and includes species with (±) systemic haplophase mycelium on the cone scales of spruce and dikaryophase on Ericaceae subfam. Pyroloideae (syn. Pyrolaceae): R. monesis, R. pyrolae (syn. Chrysomyxa pirolatum), and R. ramischiae. Savile (1950) emphasised the importance of the size and spacing of the warts on the surface of aeciospores in distinguishing the species.

In Central Europe, Chrysomyxa species are mainly distributed in the montane forests of the Alps and the low mountain ranges. The wax-like crust-forming telia develop on overwintering leaves.

1 Chrysomyxa abietis (Wallr.) Unger

Fig. 6a, b

Syn. Blennoria abietis Wallr.

Micro-form:

III on: Picea abies, (P. engelmannii, P. pungens, P. sitchensis)

Spermatogonia absent. – Telia on transverse orange or yellow bands on the needles, hypophyllous, elongate, 0.5–10 mm long, 0.3–0.5 mm broad, 0.5 mm high, orange to reddish-brown. – Teliospores in chains 70–120 µm long, single spores 20–30 × 10–14 µm, oblong; wall hyaline, smooth, 1 µm thick; contents orange; basidium 4-celled. – References: Gäumann (1959: 101), Wilson and Henderson (1966: 59).

Remarks. The hyphae of Chrysomyxa abietis, growing first in the intercellular space of the mesophyll, invade also the mesophyll cells in autumn, and start producing teliospores (Grill et al. 1984). The spores mature in spring and germinate without any period of rest. This rust may cause considerable defoliation of spruce. The infection is heaviest in dense stands of young trees.

This rust is also recorded on Picea engelmannii, P. pungens and P. sitchensis from Norway, Scotland and Ireland (Wilson and Henderson 1966; Gjærum 1974). According to Gäumann (1959), these records need revision. In N America P. engelmannii and P. pungens serve as hosts of the similar Ceropsora weirii (H.S. Jacks.) Aime & McTaggart (syn. Chrysomyxa w.). Its life cycle resembles that of Ch. abietis. – For the distribution of Ch. abietis in Austria see Poelt and Zwetko (1997: 48).

2 Chrysomyxa empetri (Pers.) J. Schröt.

Fig. 6c

Heteropsis-form with secondary aecia:

(0,Ia on: Picea abies?, P. glauca)

Ib,III on: Empetrum hermaphroditum, (E. nigrum)

Spermatogonia on needles of current season, amphigenous, in one row, conspicuous, yellowish then reddish-brown, subepidermal, 140–160 µm broad, 100–135 µm deep. – Primary aecia on needles of current season, amphigenous, in one row, on pale-yellowish portions, elliptical to subcircular in transverse section, 0.5–1.5 mm wide, 0.5–2 mm high; peridium hyaline, rupturing at apex; peridial cells 19–54 × 32–76 µm, polygonal, elongate vertically; outer walls smooth, about 1 µm thick, inner walls coarsely verrucose, 4–5 µm thick. – Primary aeciospores 21–34 × 30–47(–55) µm, ellipsoid or ovoid, yellow; wall closely and coarsely verrucose, 0.3–1.5 µm thick excluding the warts. – Secondary aecia (uredinia) epiphyllous, one or few on a leaf, pustular, subepidermal, circular or elliptical to linear, 0.2–2 mm long; peridium distinct, adhering to the epidermis which ruptures at maturity; peridial cells in a single layer, angular, 10–20 µm in diam.; wall 3–4 µm thick. – Secondary aeciospores (urediniospores) catenulate, 25–49 × 20–31 µm, pulverulent, ellipsoid, ovoid or subgloboid, orange; wall hyaline, closely and coarsely verrucose, 0.2–1 µm thick, excluding the warts; warts cylindrical to slightly stellate or irregular, 0.7–2.2 µm high, 0.3–1.0 µm wide, 0.7–2.5(–3) µm spacing. – Telia epiphyllous on overwintered leaves, one or few on a leaf, yellow, cushion-shaped, wax-like, subepidermal, subcircular to elongate, often nearly as long as the leaf. – Teliospores catenulate, 3–6 in a chain, 19–24 × 18–21 µm, thin-walled, smooth; contents yellow. – Basidia 4-celled, pale yellow, up to 65 µm long, 7–8 µm in diam. – Basidiospores 10–15 µm in diam., usually about 12 µm, subgloboid to ellipsoid, very thin-walled, with yellow contents. – References: Gäumann (1959: 99–101), Wilson and Henderson (1966: 60), Termorshuizen and Swertz (2011: 158).

Remarks. According to Gäumann (1959), Chrysomyxa empetri is widespread in Eurasia and N America, but telia are recorded rather infrequently; in some areas only secondary aecia are known. – For records of Ch. empetri in Austria see Poelt and Zwetko (1997: 48–49).

3 Chrysomyxa ledi (Alb. & Schwein.) de Bary

Fig. 7

Syn. Chrysomyxa ledi (Alb. & Schwein.) de Bary var. ledi s. Savile (1950, 1955b)

Heteropsis-form with secondary aecia:

(0,Ia on: Picea abies, P. engelmannii, P. glauca, P. mariana)

Ib,III on: Rhododendron tomentosum? [syn. Ledum palustre]

Spermatogonia on current-year needles, single or in small groups, amphigenous, subepidermal, 100–190 µm wide, 90–150 µm high, orange coloured, in median section concave to slightly flattened. – Primary aecia on current-year needles, amphigenous, in one or two longitudinal rows, on yellow spots, tubular, 0.3–1.3 mm wide; peridium dehiscing at apex, later shredding, leaving a fringe around the sorus; outside of cells deeply concave, ± smooth; inside of cells shallowly concave, shallowly and densely warted, warts often arranged in undulating rows; lateral margins broad (3–6 µm or more) with coarse striations. – Primary aeciospores 20–38 × 15–28 µm (x = 28.0±4.1 × 21.6±2.4 µm), ovoid, ellipsoidal, globose, or subglobose, with a distinct narrow longitudinal groove; wall hyaline, 0.8 µm thick; wall plus warts 1.6–4.9 µm thick; warts crowded, annulate, tapering. – Secondary aecia (uredinia) hypophyllous on leaves of previous year, orange-red, later fading, occasionally caulicolous, circular, 0.2–0.3 mm wide, single or in groups; peridium of two or three layers of thin-walled pseudoparenchymatous cells that are much smaller than spores. – Secondary aeciospores (urediniospores) 18–30 × 16–26 µm (x = 24.2±1.7 × 20.7±1.3 µm), globose, subglobose or ovoid, occasionally ellipsoidal, sometimes notched or flattened at one end because of a narrow longitudinal groove with or without a well-defined edge; wall hyaline, 0.5–0.8 µm thick; wall plus warts 2.5–2.9 µm thick. – Telia hypophyllous on leaves of previous year, sparsely aggregated, flat, blood red to orange-red. – Teliospores catenulate, 5–7 in a 70–90 µm long chain, 13–30 × 10–20 µm, oblong to cuboid; contents orange. – Basidio­spores 11 × 7 µm, ovoid; contents orange. – References: Gäumann (1959: 96–97), Crane (2001: 965–966).

Remarks. Chrysomyxa ledi occurs in Eurasia throughout the range of its broad-leaved hosts, independent of host alternation, in N Europe on Rhododendron tomentosum Harmaja (syn. Ledum palustre). The aecial stage is found on native and ornamental spruces, in Europe on Picea abies, P. obovata, P. engelmannii, P. glauca, P. mariana, and probably others (Crane 2001). Chrysomyxa ledi, the Eurasian hypophyllous rust on Rhododendron tomentosum, is distinct in morphology from the rusts occurring on Rhododendron subsect. Ledum in N America. SEM clearly demonstrates the morphological differences, especially of primary and secondary aeciospores, distinguishing Ch. ledi s.str. from the N American taxa, treated as separate species by Crane (2001). Five specimens from Japan (PUR) on several varieties of Ledum palustre (now all considered as Rhododendron diversipilosum) were examined by Hiratsuka et al. (1992); they also differ somewhat from the European specimens and were therefore not used to compile the species description. Their secondary aeciospores are smaller (14–25 × 11–21 µm, x = 19.4±2.7 × 14.9±2.2 µm) than those in European samples and their surface ornamentation is variable (l.c., figs 4B, 4D). Warts have broad irregular tops, and spores may have a flattened end where warts are confluent; however, there is seldom a well-defined groove. The coarser margins of the peridial cells of Ch. ledi (l.c., fig. 4H) are an important distinguishing feature between the aecial stages of Ch. ledi and Ch. rhododendri. Although Ch. ledi is not known to occur in N America, certain morphological features of rusts on Rhododendron subsect. Ledum from both continents suggest a common ancestor. The peridial cells of Ch. ledi are remarkably similar to those of Ch. ledicola (Peck) Lagerh. in N America (Crane 2000), and the peridium of both species shreds in a similar manner during aeciospore release. Chrysomyxa ledi and Ch. woroninii occur on the same host plants, but they cause different signs and symptoms on both hosts, Rhododendron subsect. Ledum and Picea (Crane et al. 2000; Crane 2001). In N Europe, rainy summers favour heavy infection of spruce by Ch. ledi (Melekhov 1946), and trees over large areas may turn bright yellow. Premature shedding of needles probably affects incremental growth. – For a record of Ch. ledi in Austria see Poelt and Zwetko (1997: 49).

4 Chrysomyxa rhododendri (DC.) de Bary

Fig. 8

Syn. Chrysomyxa ledi s.l.; Ch. ledi (Alb. & Schwein.) de Bary var. rhododendri (de Bary) Savile

Heteropsis-form with secondary aecia:

0,Ia on: Picea abies, (P. pungens)

Ib,III on: Rhododendron ferrugineum, R. hirsutum, (R. × intermedium, Rhododendron spp. cult.)

Spermatogonia on current-year needles, amphigenous, numerous, prominent, round or elongated, honey-coloured, then reddish-brown; hymenium broad and flat to shallowly concave in vertical section, 140–220 µm wide and 110–150 µm high. – Primary aecia on transverse, yellowed zones of current-year needles, causing premature defoliation, amphigenous, variable in size, 0.3–1.3 mm wide, up to 3 mm long, single or confluent; peridium delicate, irregularly torn at maturity but persistent, white; on outside, cells shallowly concave, smooth; on inside, cells convex with shallow warts, sometimes appearing labyrinthine; lateral margins narrow (about 2 µm), striate. – Primary aeciospores 18–30 × 16–22 µm (x = 23.6±2.7 × 18.6±1.5 µm), variable in shape from globoid to ellipsoid or ovoid, with one or both ends flat or with a small delicate cap, part of an indistinct longitudinal, smooth strip containing irregular shallow bumps (not always visible by light microscopy); wall hyaline, wall plus warts 2.0–3.3 µm thick; contents orange. – Secondary aecia (uredinia) hypophyllous on leaves of previous year, also on petioles, fruit pedicels and twigs, scattered, partially or completely covering underside of some leaves but absent from others, erumpent through epidermis, round, pulvinate, 0.2–0.7 mm wide, larger on twigs, flat-bottomed in vertical section; peridium inconspicuous, of collapsed, thin-walled cells. – Secondary aeciospores (urediniospores) 18–32(–36) × 14–22 µm (23.6±3.0 × 17.7±2.0 µm), mostly ellipsoid or ovoid, occasionally globoid, one or both ends slightly flattened or with a small cap which is part of a shallow longitudinal strip containing shallow, irregular bumps; contents apricot-coloured; wall hyaline, less than 1 µm thick; wall plus warts 1.2–2.9 µm thick. – Telia hypophyllous on leaves of previous year, in groups, confluent, erumpent through epidermis, larger and more irregular in shape than the secondary aecia, up to 1 mm long. – Teliospores catenulate (chains 4–6-celled in the middle of the sorus), cylindric-prismatic, 20–30 µm long, 10–14 µm wide. – References: Gäumann (1959: 94–95), Wilson and Henderson (1966: 62–63), Crane (2001: 974–975).

Remarks. Some authors synonymised Chrysomyxa rhododendri with Ch. ledi (e.g., Termorshuizen and Swertz 2011), and Savile (1950, 1955b) reduced Ch. rhododendri to a variety. On the other hand, Crane (2001) noted that the mean size of secondary aeciospores of Ch. ledi and Ch. rhododendri is very similar, but the primary aeciospores of Ch. ledi tend to be longer than those of Ch. rhododendri. Whereas Ch. ledi spores have a narrow groove and long tapered warts, those of Ch. rhododendri have an indistinct smooth or irregular longitudinal strip and only somewhat conical warts (Fig. 8c, d). The habitat differences also support the separation of these two taxa as distinct species: Ch. rhododendri occurs mainly in subalpine regions in Europe, Ch. ledi at lower elevations farther north. – For the distribution of Ch. rhododendri in Austria see Poelt and Zwetko (1997: 49–50).

(5) Chrysomyxa woroninii Tranzschel

Heteropsis-form (without secondary aecia):

(0,Ia on: Picea abies, P. glauca, P. mariana, P. pungens)

(III on: Rhododendron tomentosum [syn. Ledum palustre])

Spermatogonia not described. – Primary aecia on unfurling shoots resembling a cone or a stunted witches’ broom, golden yellow, densely and evenly distributed over the whole surface of pale, fleshy, patent needles. – Primary aeciospores (27–)33–62(–66) × (16–)21–30(–45) µm. – Telia already appearing in spring on shoots resembling a small witches’ broom, densely covering the young leaves of shooting buds. – Teliospores similar to those of Ch. ledi. – References: Crane et al. (2000: 584–586), Klenke and Scholler (2015: 689–690).

Remarks. Crane et al. (2000) clarified the life cycle of Chrysomyxa woroninii and found that it has no secondary aecia (uredinia). Infected spruce buds need almost one year before they show the typical symptoms. This rust is not listed by Poelt and Zwetko (1997) and has not been found in Central Europe so far; its distribution is circumpolar.

N.B.: Descriptions of Coleosporium species (except for C. tussilaginis s.l.) were missing in the original manuscript and supplemented in line with the species concept favoured by Peter Zwetko, following Gäumann (1959).

Coleosporium species are predominantly heteroecious with spermatogonia and primary aecia on the needles of Pinus, and secondary aecia and basidiosori on various families of angiosperms, especially Asteraceae. Many authors (e.g., Gäumann 1959; Klenke and Scholler 2015) define the secondary aecia as uredinia, and the basidiosori as telia (see remarks). Therefore, we prefer to add these alternative interpretations in parentheses.

Central European taxa were often united in a single species complex usually named ‘Coleosporium tussilaginis s. latiss.’ or ‘C. tussilaginis s.l.’ (s. Hylander et al. 1953; Brandenburger 1985; Termorshuizen and Swertz 2011, and others). Also Helfer (2013), in his critical assessment of European taxa and their distribution, accepted only formae speciales within this taxon. Beenken et al. (2017) presented molecular phylogenetic evidence for at least three distinct species complexes (or three ± broadly defined species, respectively): C. pulsatillae, C. inulae, and C. tussilaginis. For the time being, we prefer to maintain the narrowly delimited species accepted by Gäumann (1959) which are chiefly defined by host specificity in the dikaryotic stage. Coleosporium records on pines can only be assigned to a particular species by inoculation experiments, by unambiguous field observations, or by molecular genetic evidence. – Spermatogonia subepidermal, with paraphyses and flexuous hyphae (Group I, type 2 according to Cummins and Hiratsuka 2003). – Primary aecia peridermioid, foliicolous, erumpent, with prominent, tongue-shaped peridia composed of a single layer of verrucose cells, dehiscing irregularly (Fig. 9a). – Primary aeciospores catenulate, ellipsoid or globoid, with hyaline, tessellate, superficially tuberculate wall (Figs 9b, 11). – Secondary aecia (uredinia) caeomoid, usually hypophyllous, subepidermal, erumpent, pulverulent, without peridia (Fig. 10). – Secondary aeciospores (urediniospores) catenulate, globoid or oblong, in wall structure resembling the primary aeciospores (Fig. 12). – Basidiosori (telia) usually hypophyllous, subepidermal, indehiscent except through weathering, flattened, at first forming wax-like crusts, becoming gelatinous on germination (Fig. 10). – Basidia (teliospores) sessile, in a single layer in lateral contact, cylindroid, clavoid or prismatic with smooth, hyaline walls, thin at the sides, strongly thickened and gelatinous above, at first unicellular, then becoming divided into four cells, each producing a long sterigma bearing a basidiospore (Figs 13, 14). Germination occurs without dormancy in summer and autumn. – Basidiospores ovoid or ellipsoid, rather large, thin-walled, reddish-orange.

Remarks. Coleosporium species do not have true teliospores but basidia produced in telium-like crusts (basidiosori) beneath the host epidermis (e.g., Berndt 1996). The basidium is also interpreted as a teliospore (probasidium) forming an intracellular metabasidium by ‘internal germination’ (e.g., Gäumann 1959; Klenke and Scholler 2015). Wall ornamentation of primary aeciospores is rather diverse in this genus (e.g., Hiratsuka and Kaneko 1975; Kaneko 1981), but not in the European species of the C. tussilaginis complex (see below).

Two remarkable neomycetes of this genus were recorded from Austria rather recently, Coleosporium montanum (Arthur & F. Kern) McTaggart & Aime on Symphyotrichum novae-angliae (Voglmayr et al. 2020), most probably also on S. lanceolatum (Scheuer 2015, 2018, as C. asterum), and C. solidaginis (Schwein.) Thüm. on Solidago gigantea (Voglmayr et al. 2022). For an assessment of European records of C. solidaginis see Beenken et al. (2017).

1 Coleosporium tussilaginis s.l. (s. Hylander et al. 1953 and others)

Fig. 9

Syn. Peridermium oblongisporum Fuckel s.l.

Heteropsis-forms with secondary aecia (or life cycle insufficiently known):

0,Ia on: Pinus sylvestris, P. mugo, P. nigra and other two-needle pines (also cultivated species)

Collections on the following hosts could not be assigned to any known Coleosporium species within this complex:

(Ib,III* on: Clematis sp. cult., Erechtites hieraciifolius, Tropaeolum sp. cult.)

Spermatogonia on needles, amphigenous, chiefly epiphyllous on pale or yellow spots, subepidermal or subcortical, scattered or in two longitudinal rows, yellowish, becoming brown, conoid, flattened, 0.5–1 mm long, 0.2–0.5 mm wide. – Primary aecia amphigenous, laterally compressed, 1–3 mm long, 1–5 mm high, yellow becoming paler, dehiscing irregularly; peridial cells 35–70 µm long, 16–34 µm wide, walls equally thickened (3–5 µm) or external wall thicker than internal, verrucose; spore mass orange-red. – Primary aeciospores globoid, ellipsoid, obovoid or angular, 20–40 × 16–27 µm; wall hyaline, 2–3 µm thick, densely verrucose; warts (ornaments) annulate and irregularly cylindrical with a flat top (Fig. 9b) in the majority of collections, rarely(?) tapering and with ‘rootlike stilts’ (see remarks below). – Secondary aecia (uredinia) hypophyllous, scattered, rounded or oblong, 0.4–0.7 mm in diam., soon naked, pulverulent, orange-red. – Secondary aeciospores (urediniospores) globoid, ellipsoid or ovoid, 20–40 × 16–25 µm; wall hyaline, 1–1.5 µm thick, densely and finely verrucose. – Basidiosori (telia) hypophyllous, rounded, scattered or confluent, forming waxy orange-red crusts, 0.4–0.8 mm in diam. – Basidia (teliospores) clavoid to cylindrical or ± prismatic, rounded at the apex, attenuate or rounded at the base, 60–105 × 15–24 µm; at first unicellular, then becoming 4-celled and greatly thickened and gelatinous at the apex; wall thin at the sides, 12–30 µm thick at the apex, hyaline, smooth. – Reference: Wilson and Henderson (1966: 3–4).

Remarks. Spermatogonia and primary aecia of this species complex are mainly found on the needles of Pinus sylvestris, P. mugo and P. nigra (but also on other two-needle pines, including cultivated species), secondary aecia and basidiosori chiefly on the leaves and stems of Asteraceae (especially trib. Senecioneae), Campanulaceae and Orobanchaceae trib. Pedicularieae. Coleosporium records on pines can only be assigned to one of our narrowly delimited species by inoculation experiments, by unambiguous field observations, or by molecular genetic evidence.

At least the European species of this complex are quite uniform morphologically, both in the aecial and in the telial stage. Blanz and Zwetko (2018: 300, fig. 4A) confirmed the occurrence of the second, apparently rare type of wall ornamentation of primary aeciospores in Austria (on Pinus sylvestris in Lower Austria), the tapering warts with ‘rootlike stilts’ which had already been described earlier (e.g., Holm et al. 1970: Plate I). However, in the majority of collections, warts were found to be irregularly cylindrical with a flat top (e.g., Helfer 2013; Blanz and Zwetko 2018: 300, fig. 4B).

Elongate secondary aeciospores and narrow basidia as well as the divergent host range in the dikaryotic stage (Pulsatilla, Ranunculaceae) support the separation of Coleosporium pulsatillae from C. tussilaginis s.l. (e.g., Kaneko 1981). Braun (1981) pointed out that the apical wall thickening of the basidia (teliospores) separates C. inulae (Fig. 13a) and C. telekiae from the complex. Beenken et al. (2017) confirm that molecular genetic evidence supports the separation of C. pulsatillae and C. inulae as distinct species (or species complexes, respectively). Cummins (1978) revised the N American taxa on Asteraceae and considered, i.a., the size of secondary aeciospores (urediniospores), basidia and basidiospores; two of the species accepted by Cummins (l.c.) also occur in Central Europe, C. senecionis and C. sonchi.

(2) Coleosporium aposeridis P. Syd. & Syd.

Syn. Coleosporium tussilaginis s.l.; C. tussilaginis s. Braun (1981)

Life cycle insufficiently known:

(0,Ia on: Pinus?) – Klenke and Scholler (2015)

(Ib,III* on: Aposeris foetida)

Spermatogonia and primary aecia unknown. – Secondary aecia (uredinia) hypophyllous, in groups in leaf spots 2–4 mm wide, 0.2–0.4 mm in diam., golden-yellow, later fading. – Secondary aeciospores (urediniospores) polygonal-globose or polygonal-ellipsoidal, densely verrucose, 18–25 × 16–21 µm; wall hyaline, 1.5 µm thick. – Basidiosori (telia) hypophyllous, dispersed or irregularly grouped, 0.2–0.4 mm in diam., golden-yellow, more light-coloured later on. – Basidia (teliospores) cylindric-clavate, 60–80 × 15–18 µm, ± rounded at the apex; apical wall 15–25 µm thick. – Reference: Gäumann (1959: 118).

Remarks. Gäumann (1959) noted that the type location of this apparently rare rust is Carinthia, but it has been described from Slovenia (near Ljubljana/Laibach), not from Carinthia. Helfer (2013) lists Aposeris foetida as a host of Coleosporium tussilaginis f.sp. sonchi but does not mention C. aposeridis as a synonym (see below). According to Poelt and Zwetko (1997: 51–52), it has not been found in Austria so far.

3 Coleosporium cacaliae auct.

Syn. Coleosporium tussilaginis s.l.; C. tussilaginis s. Braun (1981); ?C. cacaliae G.H. Otth; C. tussilaginis (Pers.) Lév. f.sp. senecionis-silvatici Boerema & Verh. (Helfer 2013); [non Uredo cacaliae DC. = Coleosporium C. (DC.) Rabenh. = Uromyces c. (DC.) Unger]

Heteropsis-form with secondary aecia:

(0,Ia on: Pinus mugo, P. sylvestris; inoculation experiments) – Gäumann (1959)

Ib,III* on: Adenostyles alliariae, A. alpina [syn. A. glabra], (A. leucophylla)

Spermatogonia and primary aecia not described in detail. – Secondary aecia (uredinia) hypophyllous, roundish, orange. – Secondary aeciospores (urediniospores) ellipsoidal, 24–35 × 21–24 µm; wall hyaline, thin, with small, stout, bacilliform warts. – Basidiosori (telia) hypophyllous, forming red wax-like crusts. – Basidia (teliospores) prismatic, 80–140 × 18–25 µm; apical wall thickened, up to 28 µm. – References: Gäumann (1959: 117), Klenke and Scholler (2015: 81).

Remarks. Apparently the name Uredo cacaliae DC. (now Uromyces cacaliae) has been misinterpreted for ages, and a correct name for the Coleosporium species on Adenostyles is still pending. Helfer (2013) includes C. cacaliae auct. with C. tussilaginis f.sp. senecionis-sylvatici (see below under C. senecionis). – For the distribution of C. cacaliae auct. in Austria see Poelt and Zwetko (1997: 52).

4 Coleosporium campanulae (Pers.) Tul.

Figs 10a, 11a, 12a

Syn. Coleosporium tussilaginis s.l.; C. tussilaginis (Pers.) Lév. f.sp. campanulae-rapunculoidis Boerema & Verh. (Helfer 2013); C. campanulacearum Fr.; C. phyteumatis F. Wagner

Heteropsis-form with secondary aecia:

(0,Ia on: Pinus sylvestris, P. mugo, P. nigra and others; inoculation experiments) – Gäumann (1959)

Ib,III* on: Campanula barbata, C. beckiana, C. bononiensis, C. carnica, C. cespitosa, C. cochleariifolia, C. glomerata, C. latifolia, C. moravica, C. patula, C. persicifolia, C. praesignis, C. rapunculoides, C. rapunculus, C. rotundifolia, C. scheuchzeri, C. trachelium, C. witasekiana, Legousia speculum-veneris, Lobelia cardinalis, Phyteuma betonicifolium, P. orbiculare, P. spicatum, (Campanula cervicaria, C. medium, C. pulla, C. rhomboidalis, C. sibirica, C. thyrsoides, Legousia hybrida, Phyteuma nigrum)

Spermatogonia and primary aecia see above under C. tussilaginis s.l. – Primary aeciospores (usually somewhat irregularly) elongate or ellipsoidal, 23–43 × 13–19 µm; wall hyaline, 3–4 µm thick, densely ornamented with warts 1–2 µm in diam., their central points 2–2.5 µm apart. – Secondary aecia (uredinia) hypophyllous, on some hosts also on stems, roundish or irregular, orange. – Secondary aeciospores (urediniospores) subglobose to oval, often slightly polygonal, 21–35 × 14–21 µm (after Gäumann 1959), (12.0–)20.5±4.8(–30.2) × (9.0–)14.9±3.2(–26.4) µm (after Helfer 2013); wall 1.5 µm thick, ornamented with fine warts 1 µm thick, their central points 1.5–2 µm apart. – Basidiosori (telia) at first yellowish-red, later blood-red, small but confluent to form larger crusts. – Basidia (teliospores) prismatic, 50–100 × 14–28 µm; apical wall 12–35 µm thick. – References: Gäumann (1959: 113–114), Helfer (2013: 91–92).

Remarks. Several taxa or ‘biological forms’ have been described within this taxon, from ‘microspecies’ (e.g., Coleosporium campanulae-rapunculoidis Kleb., C. campanulae-trachelii Kleb.) to formae speciales (e.g., Boerema and Verhoeven 1972). The host range of these taxa, however, appears to be quite irregular. Therefore, we assume that their taxonomic value might be questionable and prefer to unite them under the traditional name C. campanulae. Helfer (2013) united all those taxa under the name C. tussilaginis f.sp. campanulae-rapunculoidis Boerema & Verh. Another species growing on Campanula, C. pseudocampanulae, has been described from the Himalaya region by Kaneko et al. (1990). – For the distribution of C. campanulae in Austria see Poelt and Zwetko (1997: 52).

5 Coleosporium cerinthes J. Schröt. [nom. inval.]

Life cycle insufficiently known:

(0,Ia on: Pinus?) – Klenke and Scholler (2015)

Ib,III* on: Cerinthe minor

Spermatogonia and primary aecia unknown. – Secon­dary aecia (uredinia) hypophyllous, pulvinate to crust-like, small, orange-yellow. – Secondary aeciospores (urediniospores) 20–40 × 16–25 µm, densely and finely verrucose. – Basidiosori (telia) crustose, wax-like, small, orange-red. – Basidia (teliospores) palisade-like, conglutinate, 60–105 × 15–24 µm, apical wall 12–30 µm thick. – References: Schröter (1887: 370), Klenke and Scholler (2015: 275–276).

Remarks. This is an unresolved taxon of questionable status, described ‘ad int[erim]’ from scanty material collected in Silesia, Poland (Schröter 1887). Urban and Marková (2009) mention a record in their rust checklist of the Czech and Slovak Republics. The only collection from Austria (also on Cerinthe minor, herbarium C. B. Schiedermayr, LI) consists of a single leaf spot with a small group of sori and may just as well be interpreted as an incidental infection by another Coleosporium species (Poelt and Zwetko 1997: 52; Zwetko 2000: 11).

6 Coleosporium doronici Namysł.

Syn. Coleosporium tussilaginis s.l.; C. tussilaginis s. Braun (1981); C. tussilaginis (Pers.) Lév. f.sp. doronici S. Helfer (Helfer 2013)

Heteropsis-form(?) with secondary aecia:

(0,Ia on: Pinus mugo agg.) – Klenke and Scholler (2015)

Ib,III* on: Doronicum austriacum, D. glaciale subsp. calcareum [syn. D. calcareum]

Spermatogonia and primary aecia unknown? – Secon­dary aecia (uredinia) hypophyllous, singly or in small groups, round, 0.3–0.5 mm in diam., golden yellow, later yellowish. – Secondary aeciospores (urediniospores) almost globose, less commonly ellipsoidal or ovoid, 22–32 × 17–27 µm (after Gäumann 1959), (10.8–)27.8±3.8(–34.1) × (7.0–)19.1±3.6(–24.8) µm (after Helfer 2013); wall hyaline, c. 1.5 µm thick, densely ornamented with coarse warts. – Basidiosori (telia) hypophyllous, dispersed or more commonly irregularly confluent, 0.4–0.7 µm in diam., golden yellow. – Basidia (teliospores) cylindric-clavate, 60–90 × 18–25 µm, rounded or narrowed at the base; apex rounded, apical wall 20–30 µm thick. – References: Gäumann (1959: 118), Helfer (2013: 92), Klenke and Scholler (2015: 352).

Remarks. Apparently this rarely recorded species prefers humid localities at montane to subalpine altitudes (Poelt and Zwetko 1997: 52–53).

7 Coleosporium euphrasiae (Schumach.) Fuss

Figs 11b, 12b

Syn. Coleosporium tussilaginis s.l.; C. rhinanthacearum (DC.) Fr.; C. tussilaginis (Pers.) Lév. f.sp. rhinanthacearum Boerema & Verh. (Helfer 2013); Uredo rhinanthearum Link

Heteropsis-form with secondary aecia:

(0,Ia on: Pinus mugo, P. sylvestris; inoculation experiments) – Gäumann (1959)

Ib,III* on: Euphrasia officinalis, E. officinalis subsp. picta [syn. E. picta], E. officinalis agg. [syn. E. rostkoviana agg.], E. salisburgensis, E. stricta agg., Odontites vernus?, O. vulgaris [syn. O. ruber p.p.], O. vulgaris agg. [O. ruber agg.], Rhinanthus alectorolophus agg., R. aristatus agg., R. buccalis, R. × digeneus, R. glacialis, R. minor, R. serotinus, R. serotinus agg., (Bartsia alpina?, Euphrasia hirtella, E. kerneri, E. micrantha, E. minima, E. nemorosa, E. nemorosa × stricta, Odontites luteus, Pedicularis palustris, Rhinanthus riphaeus [syn. R. pulcher])

Spermatogonia and primary aecia see above under C. tussilaginis s.l. – Primary aeciospores ± oval, often globose, rarely more elongate, 15–35 × 15–24 µm; wall 2–3 µm thick; warts 1–2 µm wide but sometimes confluent, their central points 2–3 µm apart. – Secondary aecia (uredinia) hypophyllous, 0.5 mm in diam., orange-yellow. – Secondary aeciospores (urediniospores) roundish or oval, rarely more elongate, partly polygonal, 18–29 × 13–18 µm (after Gäumann 1959), (19.2–)22.9±2.0(–28.4) × (14.1–)17.9±1.7(–22) µm (after Helfer 2013); wall c. 1 µm thick; warts c. 1 µm thick, their central points 1.5–2 µm apart. – Basidiosori (telia) mainly hypophyllous but also on stems and calyces, rather thick, wax-like, orange-red. – Basidia (teliospores) prismatic, 68–105 × 15–24 µm; apical wall 10–15 µm thick. – References: Gäumann (1959: 110), Helfer (2013: 94–95).

Remarks. The ultrastructure of the D-haustoria of Coleosporium euphrasiae is very characteristic and may distinguish this species from others (Berndt 1996). This rust is apparently widespread but locally uncommon. Because the ‘telial’ hosts are almost exclusively annual herbs of Orobanchaceae trib. Pedicularieae we may assume that its occurrence on these hosts is strictly dependent on host alternation. For the disputable nomenclature see Laundon (1975). – For the distribution of C. euphrasiae in Austria see Poelt and Zwetko (1997: 53).

8 Coleosporium inulae Rabenh.

Figs 10b, 11c, 12c, 13a

Syn. Coleosporium tussilaginis s.l. (s. Hylander et al. 1953 and others); C. tussilaginis (Pers.) Lév. f.sp. inulae S. Helfer (Helfer 2013)

Heteropsis-form with secondary aecia:

(0,Ia on: Pinus sylvestris; inoculation experiments) – Gäumann (1959)

Ib,III* on: Inula helenium, Pentanema ensifolium [syn. Inula ensifolia], P. salicinum [syn. I. salicina], (P. germanicum [syn. I. germanica])

Spermatogonia and primary aecia see above under C. tussilaginis s.l. – Primary aeciospores mainly elongate, only few subglobose or oval, 20–40 × 13–18 µm; wall hyaline, 3–3.5 µm thick, densely verrucose; warts 1–2 µm thick, their central points 2–2.5 µm apart. – Secondary aecia (uredinia) hypophyllous, causing small yellowish leaf spots, up to 0.5 mm in diam., bright orange-yellow. – Secondary aeciospores (urediniospores) usually elongate-oval or elongate, rarely ± globose, often somewhat polygonal, 19–30 × 12–15 µm (after Gäumann 1959), (21.2–)30.3±3.3(–39.5) × (15.7–)23.4±3.1(–30.7) µm (after Helfer 2013); wall hyaline, c. 1.5 µm thick; warts c. 1 µm wide, their central points 1–1.5 µm apart. – Basidiosori (telia) hypophyllous, forming small crusts up to 1 mm in diam., at first yellow, later red. – Basidia (teliospores) prismatic, 90–110 × 16–22 µm; apical wall 35–40 µm thick. – References: Gäumann (1959: 119–120), Helfer (2013: 92–93).

Remarks. Braun (1981) has drawn attention to the conspicuously thickened apical wall of the basidia (teliospores), a useful diagnostic character. Beenken et al. (2017) confirm that also molecular genetic evidence clearly supports the separation of Coleosporium inulae as a distinct species. – For records of C. inulae in Austria see Poelt and Zwetko (1997: 53).

(9) Coleosporium ligulariae Thüm.

Syn. Coleosporium tussilaginis s.l.; C. inulae Rabenh. s. Braun (1981); C. tussilaginis (Pers.) Lév. f.sp. senecionis-silvatici Boerema & Verh. (Helfer 2013)

Life cycle insufficiently known:

(0,Ia on: Pinus?) – Klenke and Scholler (2015)

(Ib,III* on: Ligularia sibirica)

Spermatogonia and primary aecia unknown. – Secon­dary aecia (uredinia) hypophyllous, orange, 0.5 mm in diam. – Secondary aeciospores (urediniospores) 21–36 × 16–26 µm, verrucose. – Basidiosori (telia) red, densely grouped, forming wax-like crusts. – Basidia (teliospores) palisade-like, conglutinate, 70–110 × 19–28 µm; apical wall 25–40 µm thick. – References: Azbukina (1974: 182), Kuprevič and Uljaniščev (1975: 115–116), Klenke and Scholler (2015: 515).

Remarks. Hylander et al. (1953) treated Coleosporium ligulariae as a synonym of C. senecionis (DC.) Kickx, and the latter as a race of C. tussilaginis s.l. Similarly, Helfer (2013) includes C. ligulariae with C. tussilaginis f.sp. senecionis-sylvatici (see below under C. senecionis). In Europe, C. ligulariae is reported on cultivated Ligularia species from botanical gardens (e.g., Hylander et al. 1953). Poelt and Zwetko (1997) do not mention C. ligulariae, but this rust species is widespread in Siberia and its natural range reaches Europe in Finland and Romania (Gäumann 1959).

10 Coleosporium melampyri (Rebent.) Tul.

Figs 11d, 12d, 13b

Syn. Coleosporium tussilaginis s.l.; C. tussilaginis (Pers.) Lév. f.sp. melampyri Boerema & Verh. (Helfer 2013)

Heteropsis-form with secondary aecia:

(0,Ia on: Pinus sylvestris, P. mugo; inoculation experiments) – Gäumann (1959)

Ib,III* on: Melampyrum arvense agg., M. nemorosum, M. nemorosum agg., M. pratense agg., M. sylvaticum agg., (M. cristatum)

Spermatogonia and primary aecia see above under C. tussilaginis s.l. – Primary aeciospores usually oval, more rarely subglobose or elongate, 22–35 × 17–24 µm; wall 3–4 µm thick; warts 1–2 µm wide, their central points 1.5–2 µm apart. – Secondary aecia (uredinia) hypophyllous, orange-yellow, c. 0.5 mm in diam. – Secon­dary aeciospores (urediniospores) subglobose, oval or elongate, often somewhat polygonal, 14–35 × 12–28 µm (after Gäumann 1959), (20.6–)25.9±2.6(–32.4) × (13.3–)18.9±2.2(–24.2) µm (after Helfer 2013); wall hyaline, thin; warts c. 1.5 µm thick, their central points 1.5–2 µm apart. – Basidiosori (telia) hypophyllous, occasionally in groups, wax-like, red. – Basidia (teliospores) prismatic, 70–115 × 14–28 µm; apical wall 10–28 µm thick. – References: Gäumann (1959: 112), Helfer (2013: 93).

Remarks. As the ‘telial’ hosts are annual herbs we may assume that the occurrence of Coleosporium melampyri on these hosts is dependent on host alternation. – For the distribution of C. melampyri in Austria see Poelt and Zwetko (1997: 53).

11 Coleosporium petasitis (DC.) Berk.

Fig. 12e

Syn. Coleosporium tussilaginis s.l.; C. tussilaginis U. Braun (1981); C. petasitidis (DC.) Thüm. (orthogr. var.); C. tussilaginis (Pers.) Lév. f.sp. petasitis Boerema & Verh. (Helfer 2013)

Heteropsis-form with secondary aecia:

(0,Ia on: Pinus sylvestris; inoculation experiments) – Gäumann (1959)

Ib,III* on: Petasites albus, P. hybridus, P. paradoxus

Spermatogonia and primary aecia see above under C. tussilaginis s.l. – Secondary aecia (uredinia) hypophyllous, orange, c. 0.5 mm in diam. – Secondary aeciospores (urediniospores) ellipsoid or ovoid, 21–32(–42) × 14–21 µm (after Gäumann 1959), (18.4–)26±2.3(–31.6) × (14.3–)20.7±2.2(–26.6) µm (after Helfer 2013); wall 1.5 µm thick, hyaline; warts short-bacilliform, up to 1.25 µm thick, their central points c. 1.5 µm apart. – Basidiosori (telia) forming small red crusts c. 0.5 mm in diam., in groups or confluent. – Basidia (teliospores) prismatic, 60–100 × 14–24 µm, apical wall 17–20 µm thick. – References: Gäumann (1959: 121), Helfer (2013: 93–94).

Remarks. According to Klenke and Scholler (2015), Coleosporium petasitis is common in the montane to subalpine belt. Therefore, we presume that primary aecia could also be found on Pinus mugo. – For the distribution of C. petasitis in Austria see Poelt and Zwetko (1997: 53–54).

12 Coleosporium pulsatillae (F. Strauss) Lév.

Figs 10c, 11e, 12f, 14

Syn. Coleosporium tussilaginis s.l. (s. Hylander et al. 1953 and others); C. tussilaginis (Pers.) Lév. f.sp. pulsatillae Boerema & Verh. (Helfer 2013)

Heteropsis-form with secondary aecia:

(0,Ia on: Pinus sylvestris; inoculation experiments) – Gäumann (1959)

Ib,III* on: Pulsatilla grandis, P. oenipontana, P. pratensis subsp. nigricans, P. styriaca, P. vulgaris, (P. alpina, P. vernalis)

Spermatogonia and primary aecia see above under C. tussilaginis s.l. – Primary aeciospores usually irregular-oval, 25–40 × 16–24 µm; wall 3.5–4.5 µm thick, with small thinner spots; warts c. 1 µm in diam. – Secon­dary aecia (uredinia) hypophyllous, bright yellow-orange, 0.5–1 mm in diam., surrounded by remnants of the ruptured epidermis. – Secondary aeciospores (urediniospores) usually oblong or clavate, somewhat blunt-polygonal, occasionally irregularly ellipsoidal or oval, 18–50 × 10–15 µm (Gäumann 1959), (20.8–)28.7±4.2(–40.3) × (15.5–)19.6±2.2(–24.4) µm (Helfer 2013); wall thin, >1 µm, covered with fine warts. – Basidiosori (telia) hypophyllous, blood-red, forming cushion-like crusts covered by the epidermis, c. 0.5 mm in diam. – Basidia (teliospores) cylindrical-prismatic, 65–100 × 10–22 µm; lateral walls thin, apical wall < 15 µm thick. – Basidiospores c. 8 µm. – References: Gäumann (1959: 108–110), Helfer (2013: 94).

Remarks. This is a well separated, distinctive Coleosporium species, the only one on a genus of Ranunculaceae in Europe; see Beenken et al. (2017) for molecular phylogenetic data. Due to its peculiar host range and a few morphological characters, it has been separated from the traditional ‘C. tussilaginis s.l.’ before (e.g., Kaneko 1981). The basidia and the secondary aeciospores are narrower in proportion than those of other Coleosporium species in Central Europe, but the measurements seem quite divergent in the literature (see above). More Coleosporium species on Ranunculaceae are known from Asia. – For records of C. pulsatillae in Austria see Poelt and Zwetko (1997: 54).

13 Coleosporium senecionis (Schumach.) Fr.

Figs 10d, 11g, 12g, 13c

Syn. Coleosporium tussilaginis s.l.; C. tussilaginis s. Braun (1981); C. senecionis (Pers.) Lév. f.sp. senecionis-silvatici Wagner ex Gäum.; C. tussilaginis f.sp. senecionis-silvatici Boerema & Verh. (Helfer 2013)

Heteropsis-form with secondary aecia:

(0,Ia on: Pinus sylvestris, P. mugo, P. nigra; inoculation experiments) – Gäumann (1959)

Ib,III* on: Senecio cordatus, S. doria agg., S. germanicus, S. hercynicus, S. jacobaea, S. nemorensis agg., S. ovatus, S. rupestris, S. sarracenicus, S. subalpinus, S. sylvaticus, S. umbrosus, S. viscosus, S. vulgaris, Tephroseris longifolia, (Calendula officinalis?, Pericallis cruenta cv. [syn. Senecio cruentus], S. doria, S. doronicum, S. erucifolius, S. paludosus, S. vernalis)

Spermatogonia and primary aecia see above under C. tussilaginis s.l. – Primary aeciospores either oval or elongate-oval to elongate, only few subglobose, 20–50 × 15–25 µm; wall 3–4 µm thick, coarsely verrucose; warts 1–2 µm thick, their central points 2–2.5 µm apart. – Secondary aecia (uredinia) hypophyllous, rarely epiphyllous, often on stems, up to 1 mm in size, bright yellow-orange. – Secondary aeciospores (urediniospores) in short chains, bright yellow-orange, mostly elongate or oval, (17–)22–27(–34) × (14–)18–22(–27) µm, mean 25 × 21.5 µm (after Gäumann 1959); wall 1–2 µm thick, finely verrucose; warts c. 1.5 µm apart. – Basidiosori (telia) hypophyllous and on stems, up to 1 mm in size, often in large groups and ± confluent, forming red cushions or crusts. – Basidia (teliospores) prismatic, up to 100 × 18–24 µm; apical wall up to 22 µm thick. – References: Gäumann (1959: 122), Helfer (2013: 95).

Remarks. Helfer (2013) treats this taxon under Coleosporium tussilaginis f.sp. senecionis-silvatici Boerema & Verh. and includes C. cacaliae auct. and C. ligulariae. However, his measurements of secondary aeciospores (urediniospores) are very similar, (18.6–)25.7±3.2(–37.1) × (11.8–)18.7±2.2(–26.4) µm. Further Coleosporium species on Senecio have been recorded in Asia (e.g., Kaneko 1981; Kaneko et al. 1990). – For numerous records of C. senecionis in Austria see Poelt and Zwetko (1997: 54).

According to Klenke and Scholler (2015), the Coleosporium on Calendula officinalis should be separated as C. calendulae Speg., a species rarely recorded in Germany (secondary aeciospores mostly 22–27 × 18–22 µm, finely verrucose). Helfer (2013) did not mention this taxon.

14 Coleosporium sonchi (F. Strauss) Lév. [nom. inval.]

Figs 11f, 12h

Syn. Coleosporium tussilaginis s.l.; C. tussilaginis s. Braun (1981); C. tussilaginis (Pers.) Lév. f.sp. sonchi Boerema & Verh. (Helfer 2013); C. sonchi (Schumach.) Lév. ex Tul.

Heteropsis-form with secondary aecia:

(0,Ia on: Pinus sylvestris; inoculation experiments) – Gäumann (1959)

Ib,III* on: Emilia sonchifolia cult., Sonchus arvensis, S. arvensis subsp. uliginosus, S. asper, S. oleraceus, (Crepis tectorum, Lapsana communis, Lactuca muralis [syn. Mycelis m.], Sonchus palustris)

Spermatogonia and primary aecia see above under C. tussilaginis s.l. – Primary aeciospores short-ellipsoidal to blunt-polyhedral, 25–32 × 18–25 µm; wall hyaline, 2–3 µm thick, coarsely verrucose, central points of the warts 2–2.5 µm apart. – Secondary aecia (uredinia) hypophyllous, c. 0.5 mm in diam., bright yellow-orange. – Secondary aeciospores (urediniospores) 18–27 × 14–20 µm µm (after Gäumann 1959), (15.9–)21.8±2.5(–29.6) × (9.6–)17.2±3.0(–23.9) µm (after Helfer 2013); wall 1–1.5 µm thick; warts c. 1 µm thick, their central points 1–1.5 µm apart. – Basidiosori (telia) forming small flat red crusts, often in large groups. – Basidia (teliospores) prismatic, 60–100 × 13–24 µm; apical wall 15–20 µm thick. – References: Gäumann (1959: 126), Helfer (2013: 96).

Remarks. Helfer (2013) treats this taxon under Coleosporium tussilaginis f.sp. sonchi Boerema & Verh., a form restricted to Asteraceae trib. Cichorieae. He also lists Aposeris foetida as a host of this forma specialis, but does not mention C. aposeridis as a synonym. – For records of C. sonchi in Austria see Poelt and Zwetko (1997: 54–55).

15 Coleosporium telekiae Thüm.

Syn. Coleosporium tussilaginis s.l.; C. tussilaginis (Pers.) Lév. f.sp. telekiae S. Helfer (Helfer 2013)

Life cycle insufficiently known:

(0,I on: Pinus?) – Klenke and Scholler (2015)

Ib,III* on: Telekia speciosa

Spermatogonia and primary aecia unknown. – Secondary aecia (uredinia) hypophyllous, in yellowish or brown spots, dispersed or in irregular groups, 0.3–0.6 mm in diam., golden-yellow, later pallid. – Secondary aeciospores (urediniospores) subglobose to ellipsoidal, ovoid or elongate 18–28 × 16–22 µm (after Gäumann 1959), (15.8–)22.6±3.0(–31.8) × (10.6–)17.2±2.4(–24.1) µm (after Helfer 2013); wall hyaline, 1–1.5 µm thick, densely verrucose. – Basidiosori (telia) hypophyllous, dispersed or in irregular groups, ± circular, 0.4–0.6 mm in diam., golden yellow, later pale yellowish. – Basidia (teliospores) cylindrical or slightly clavate, 80–130 × 19–25 µm; apex rounded, apical wall 25–35 µm thick. – References: Gäumann (1959: 127), Helfer (2013: 96).

Remarks. The host plant of Coleosporium telekiae, Telekia speciosa, has been introduced from E Central Europe and is now locally naturalised. – For records of C. telekiae in Austria see Poelt and Zwetko (1997: 55).

16 Coleosporium tussilaginis (Pers.) Tul. s.str.

Figs 11h, 12i, 15

Syn. Coleosporium tussilaginis (Pers.) Lév. f.sp. tussilaginis (Helfer 2013)

Heteropsis-form with secondary aecia:

(0,Ia on: Pinus sylvestris, P. mugo, P. nigra and others; inoculation experiments) – Gäumann (1959)

Ib,III* on: Tussilago farfara

Spermatogonia and primary aecia see above under C. tussilaginis s.l. – Primary aeciospores mostly oval, sometimes subglobose, less commonly elongate, 15–24(–35) × 15–24 µm; wall 2–2.5 µm thick, warts 1–1.5 µm thick, their central points 2–2.5 µm apart. – Secondary aecia (uredinia) hypophyllous, up to 0.5 mm in diam., in dispersed or ± aggregated groups, bright orange-yellow. – Secondary aeciospores (urediniospores) mostly oval, also subglobose or somewhat elongate or irregular, 22–32 × 15–22 µm (Gäumann 1959), (21.7–)28.3±3.2(–39.6) × (15.9–)20.8±2.4(–26.6) µm (Helfer 2013); wall c. 1.5 µm thick, evenly coarsely verrucose; warts >1 µm thick, their central points c. 1.5 µm apart. – Basidiosori (telia) hypophyllous, red, filling the intercellular spaces in the mesophyll, small but ± confluent and sometimes covering the whole lower leaf surface. – Basidia (teliospores) prismatic, 60–140 × 15–28 mm, apical wall 10–21 µm thick. – References: Gäumann (1959: 128–129), Helfer (2013: 90–91).

Remarks. This is presumably the most commonly recorded Coleosporium species in Austria (Poelt and Zwetko 1997: 55).

Syn. Endocronartium Y. Hirats.; Peridermium (Link) J.C. Schmidt & Kunze p.p.

N.B.: In contrast to the original manuscript, the anamorph genus Peridermium is now included in this genus. The corresponding passages concerning Peridermium and Peridermium pini (Cronartium P.) have been re-arranged and inserted here.

Cronartium is a genus with some representatives of economic importance, and two of them have been confirmed from Austria. – Diagnosis (e.g., Brandenburger 1985: 1028): Spermatogonia subepidermal, intracortical. – Aecia peridermioid, at first intraepidermal, later erumpent. – Aeciospores formed in chains with intercalary cells. – Uredinia subepidermal; peridium opening with an apical pore. – Urediniospores stipitate, formed singly. – Telia subepidermal (originating from empty uredinia), column-like, consisting of long, conglutinate chains of 1-celled teliospores. – Teliospores germinate readily with 4-celled phragmobasidia.

The name Peridermium has been widely used for aecial states of Cronartium, but also for those of other teleomorphic genera producing peridermioid aecia on conifers (e.g., Chrysomyxa, Coleosporium, Pucciniastrum s.l.). Some autoecious, reportedly endocyclic Peridermium (Cronartium) taxa have been placed in the genus Endocronartium Y. Hirats. (e.g., Hiratsuka 1969), but this genus has not been broadly accepted. For instance, already Vogler and Bruns (1993) stated that accumulating molecular genetic evidence suggested that the Endocronartium species described by Hiratsuka (l.c.) belong in three separate Cronartium clades, making Endocronartium polyphyletic. Vogler and Bruns (1993: 245) concluded that “Placing rusts with divergent phylogenetic lineages into a single polyphyletic genus solely on the basis of nuclear behavior, …, is not phylogenetically advisable”. Moreover, the observations of Hiratsuka et al. (1966) on nuclear behaviour in aeciospores and their germ tubes in Peridermium harknessii J.P. Moore (the type of Endocronartium) were doubted by several authors. However, recent results of molecular genetic studies (Samils et al. 2021) confirm the existence of autoecious, possibly anamorphic (asexual) entities cautiously named ‘life cycle forms’, but not necessarily endocyclic Cronartium species. For details see below under Cronartium pini.

1 Cronartium flaccidum (Alb. & Schwein.) G. Winter

Figs 16, 17

Syn. Cronartium asclepiadeum (Willd.) Fr.; C. gentianeum Thüm.; C. paeoniae Castagne; Peridermium cornui Rostr. emend. Kleb.; Cronartium pini s.l.; Peridermium pini s.l.

Hetereu-form:

0,I on: Pinus mugo, P. sylvestris, (P. uliginosa [syn. P. × rotundata], P. uncinata)

II,III on: Gentiana asclepiadea, Impatiens balsamina cult., Paeonia sp. cult., Tropaeolum sp. cult., Vincetoxicum hirundinaria, (Asclepias syriaca, Melampyrum cristatum, M. arvense agg., M. sylvaticum agg., Myosotis laxa, Pedicularis palustris, P. sceptrum-carolinum)

Spermatogonia intracortical. – Aecia erumpent from the cortex, usually in large groups clasping around the whole branch or stem; peridium inflated, 2–8 mm long, 2–3 mm wide and 2–3 mm high, mostly of 2 cell layers. – Aeciospores subglobose-ellipsoidal or slightly polyhedral, 22–26(–30) × 16–20 µm; wall hyaline, verrucose but with a nearly smooth strip showing only a network of fine furrows; warts bacilliform (annulate in SEM), their central points 1.5–2 µm apart; verrucose wall area 3–4 µm thick, smooth area 2–3 µm. – Uredinia hypophyllous, evenly dispersed in yellow leaf spots, up to 0.25 mm in diam., pustule-like, opening with an apical pore. – Urediniospores ovate or ellipsoidal, 21–27 × 15–20 µm; wall hyaline, 1.5–2 µm thick; warts acute, 2.5–4 µm apart. – Telia (teliospore columns) in groups or rarely evenly dispersed over the whole leaf surface, yellow-brown or brown, horn-like when dry, 1–2 mm long, 60–130 µm thick. – Teliospores ellipsoidal or elongate, 26–56 × 9–14 µm, with thin walls. – Basidiospores subglobose, c. 8 µm in diam. – Reference: Gäumann (1959: 81).

Remarks. Two formae speciales are separated by their main host species in the telial stage, Cronartium flaccidum f.sp. flaccidum on Vincetoxicum hirundinaria and f.sp. gentianeum on Gentiana asclepiadea. Both forms, however, are able to infect quite a number of unrelated dicotyledons, a highly divergent feature in rust fungi. – For the distribution of both f.sp. in Austria see Poelt and Zwetko (1997: 57–58).

Klebahn (1914) observed that in Cronartium ribicola the aeciospore wall is thicker on the smooth side (3–3.5 µm) than on the verrucose side (2–2.5 µm), whereas in C. flaccidum the verrucose side has a thicker wall (3–4 µm) than the nearly smooth side (2–3 µm). According to Klebahn’s interpretation, the smooth strip on the aeciospore surface of C. ribicola is produced by fusion of warts, whereas in C. flaccidum the warts on the nearly smooth strip are distinctly broader with narrow spacing visible as a network of fine furrows.

2 Cronartium pini (Willd.) Jørst. s.str.

Syn. Aecidium pini (Willd.) Pers. ex J.F. Gmel.; Peridermium pini (Willd.) J.C. Schmidt & Kunze s.str.; Endocronartium pini (Willd.) Y. Hirats.

Life cycle insufficiently known (anamorphic taxon or endo-form?):

0,I on: Pinus nigra?, P. sylvestris?, (P. mugo)

Spermatogonia and aecia as in Cronartium flaccidum.

Remarks. The name Peridermium pini (or Cronartium pini, respectively) has been used for both the aecial stage of Cronartium flaccidum and for a closely related, morphologically indistinguishable pine-to-pine rust. Already Klebahn (1890a) divided Peridermium pini into two species: P. pini (Willd.) Lév. emend. Kleb. and P. cornui Rostr. emend. Kleb. The latter was recognised as the anamorph of the heteroecious rust C. flaccidum, the former was frequently found on sites where the known telial host of C. flaccidum was rare or absent. The first successful infection experiments with pine-to-pine forms of Peridermium pini have been reported by Haack (1914). The only infectious spores known from P. pini (and similar autoecious pine rusts) are aeciospores, which again infect pines.

Hiratsuka et al. (1966) observed that young, immature aeciospores of Peridermium harknessii J.P. Moore (Endocronartium h., ?Cronartium quercuum) have two nuclei and that mature spores have only one. In the developing germ tubes, they found two, three or four nuclei. They concluded that nuclear fusion occurs in the aeciospores and meiosis in the developing germ tubes, i.e., the number of nuclei was considered as evidence for nuclear fusion and meiosis, although no actual phases of meiotic division in the germ tubes were reported. Functionally such aeciospores would represent teliospores and the germ tubes basidia. The reliability of this report and the justification of the subsequently described endocyclic genus Endocronartium Y. Hirats. (e.g., Hiratsuka 1969) have been questioned by various authors (Laundon 1976; Epstein and Buurlage 1988; Vogler and Bruns 1993; Vogler et al. 1997; Kaitera et al. 1999; Hantula et al. 2002).

When Hiratsuka (1968) extended his studies on Cronartium flaccidum and Peridermium pini, he found that the functionally different aeciospores of the two taxa can be distinguished morphologically by their germ tubes. In contrast, Kaitera et al. (1999) also examined morphological variation of Peridermium pini and C. flaccidum aeciospores and their germ tubes and found no diagnostic differences. Hantula et al. (2002: 203) wrote “According to previous molecular and morphological analyses, Cronartium flaccidum and Peridermium pini are very closely related despite differences in their life-cycles. ... Analyses of genetic variation suggested that pine rusts C. flaccidum and P. pini belong to the same species.” According to Hantula et al. (2002), the two rusts do not differ in symptomatology and aeciospore morphology, and can only be separated by inoculation experiments. However, more recent molecular genetic evidence from N Fennoscandia (Samils et al. 2021) showed “that the two life cycle forms are clearly differentiated and occur in separate populations. Within the life cycle forms, geographic differentiation was evident, probably due to restricted gene flow as well as connection with different alternating hosts. The host alternating form dominated in the epidemic regions in northern Fennoscandia.”

Cronartium flaccidum and C. pini cause serious diseases on two-needle hard pines in Europe. Great losses were reported from N Europe (C. pini) and Italy (C. flaccidum). The symptomatology is more conspicuous when old trees are affected. After some years the tree top becomes bare. The base of the dry and bare top of otherwise green crowns is characterised by resin flow (‘resin top’ or ‘Kienzopf’ disease). Canker (lesion) formation and resin flow on branches or stems kill parts of the crown. If the lower part of the stem is affected, the whole tree dies (e.g., Butin 1989).

For information on nomenclature and taxonomy see Laundon (1976), Hiratsuka (1995), Vogler and Bruns (1993), and Hantula et al. (2002). Whether the pine-to-pine rust Cronartium pini occurs in Austria remains uncertain (Poelt and Zwetko 1997: 58–59).

(3) Cronartium quercus (Brond.) J. Schröt. ex Arthur

Syn. Uredo quercus Brond. [in Duby]; Cronartium quercuum s. Gäumann (1959); C. quercuum s. Brandenburger (1985); ?C. asclepiadeum var. quercuum Berk.; ?C. quercuum (Berk.) Miyabe ex Shirai

Life cycle insufficiently known:

(II,III? on: Quercus petraea, Qu. pubescens, Qu. robur)

Spermatogonia and aecia wanting. – Uredinia hypophyllous, somewhat pustular, 0.25 mm in diam., opening with an apical pore, at length surrounded by the torn epidermis, yellow; peridium delicate or wanting. – Urediniospores obovoid to broadly ellipsoid, orange-yellow, 15–25 × 10–17 µm; wall hyaline, 3 µm thick, evenly echinulate with short, strong points. – Telia mostly lacking in European records. – Reference: Wilson and Henderson (1966: 3–4).

Remarks. Infection with Cronartium quercus is most frequent on sucker shoots of felled trees. This rust seems to be quite different from the American species on oak, which has larger urediniospores (20–32 × 15–20 µm). Whether it differs from the Japanese rust on oak with only slightly larger spores (24 × 19 µm), is more doubtful (Wilson and Henderson 1966). Both in Japan and in N America (see Arthur 1934), the oak rusts have been shown to have aecial stages on pines on which they form characteristic globoid galls, but these are unknown in Europe. Teliospores have been recorded once in Europe in S France (Viennot-Bourgin 1956). Cronartium quercus occurs mainly in S and W Europe, and it seems that the taxonomic affiliations of these records are still unresolved. So far, this rust has not been recorded in Austria.

4 Cronartium ribicola J.C. Fisch.

Fig. 18

Hetereuform:

0,I on: Pinus flexilis?, P. strobus, (P. aristata, P. cembra, P. koraiensis, P. monticola, P. peuce, P. wallichiana)

II,III on: Ribes alpinum, R. aureum, R. nigrum, R. rubrum, R. rubrum agg., R. uva-crispa, R. uva-crispa agg., (R. petraeum, R. sanguineum, R. spicatum)

Spermatogonia intracortical, irregular in outline, 2–3 mm in size, 34–67 µm high. – Aecia on slightly swollen parts of branches and trunks, erumpent from the cortex, often in large groups clasping around the whole branch or stem; peridium inflated, 2–7 mm long, 2–3 mm wide and 2–2.5 mm high, of 2 or 3 cell layers; outer cell walls c. 5 µm thick, smooth in the upper part of the peridium. – Aeciospores oval, subglobose or slightly polyhedral, 22–29 × 18–20 µm; wall hyaline, verrucose but with a nearly smooth area with fused warts; warts bacilliform (annulate in SEM), their central points 1.5–2 µm apart; verrucose wall area 2–2.5 µm thick, smooth area thicker, 3–3.5 µm. – Uredinia hypophyllous, evenly dispersed in yellow leaf spots; peridium opening with an apical pore. – Urediniospores oval, usually somewhat irregular, 21–25 × 13–18 µm, more rarely elongate, c. 30 × 11 µm; wall hyaline, c. 1.5 µm thick; warts acute, 2–3 µm apart. – Telia (teliospore columns) evenly dispersed in large groups, later often over the whole leaf surface, yellowish-brown, 1–1.5 mm long, 60–130 µm thick. – Teliospores 35–70 × 11–21 µm. – Reference: Gäumann (1959: 85–86).

Remarks. Cronartium ribicola has made the cultivation of Pinus strobus and related pine species impossible in Central Europe. Its epidemic spread was depicted in detail by Gäumann (1959). In some years, considerable damage was also observed on the telial hosts, especially on Ribes nigrum. Records on Pinus are much less common than on Ribes (Poelt and Zwetko 1997: 58), but in such cases this might also be due to the lack of herbarium documentation. The aecial hosts observed in the nursery of the Botanical Garden in Graz were young five-needle pines identified as Pinus cf. flexilis (det. Erwin Gruber) and P. cf. strobus.