Melampsora allii-populina : a. On Allium ascalonicum: aeciospores, spore wall sometimes thinner at certain spots; b–d. On Populus nigra: b. Urediniospores echinulate but apically smooth, wall thinner at some spots but without equatorial thickening as in M. laricis-populina; c. Paraphyses with evenly thick walls, size of an urediniospore in comparison; d. Hypophyllous uredinia and telia on Populus × canadensis; e. Teliospores arranged in subepidermal crust, spore walls evenly thick; (a, b, c, e from Klebahn 1914: 766; d by Julia Kruse).