Key to Danish species of Diderma Pers.

1 Peridium two-layered, outermost layer eggshell-like, inner layer thin and membraneous, the two layers closely connected or separated (breaks irregulaly at maturity). Sporocarps or plasmodicarps. (subgen. Diderma). 2
1' Peridium three-layered, outer layer cartilaginous, separated from the innermost layer by lime granules (breaks open in a stellate fashion at maturity). Sporocarps (subgen. Leangium). 13
2   (1) Mostly plasmodiocarps. 3
2' Mostly sporocarps (at most 1.5 times as long as broad). 5
3   (2) Plasmodiocarps thin, up to 0.1 mm, may appear as perforated plates. Diderma saundersii (Berk. & Broome ex Massee) Lado
3' Plasmodiocarps thicker, more than 0.2 mm., elongated. Occasionally accompanied by sporocarps. Rarely forming perforated plates. 4
4   (3) Spores pale violet-brown to almost colourless in transmitted light, finely warted, 7-9 µm in diam. Mostly short plasmodiocarps, often also sporocarps. D. effusum (Schwein.) Morgan
4' Spores rather dark brown, finely spinulose, 9-10 µm in diam. Oblong to ± ring-shaped plasmodiocarps. D. deplanatum Fr.
5   (2) Sporocarps sessile. 6
5' Sporocarps stipitate, occasionally the stalk is very short and hidden in the umbilicus of the sporocarp. 10
6   (5) Sporocarps brick-red to rust-brown, closely gathered, often heaped. D. simplex (J. Schröt.) G. Lister
6' Sporocarps white to beige or pale rose, sessile, solitary or closely gathered but not heaped. 7
7   (6) Perial layers clearly separated, outer layer forms a smooth lime-shell. Sporocarps white to delicate rose, ± flattened. 8
7' Perial layers closely applied, appearing as one, outer layer smoth or rough. Sporocarps white, almost spherical. 9
8   (7) Sporocarps closely gathered, often accompanied by plasmodiocarps, white. D. effusum (Schwein.) Morgan
8' Sporocarps solitary, no plasmodiocarps, white to pale rose and then quickly fading to whitish. D. testaceum (Schrad.) Pers.
9   (7) Hypothallus mostly a thick lime crust with the sporocarps embedded. The peridial layers closely connected. Spores with large, scattered warts. D. spumarioides (Fr.) Fr.
9' Hypothallus membraneous, often with lime but never as a crust and sporocarps not embedded. Spores closely warted. D. globosum Pers.
10   (5) Sporocarps disc-shaped. D. hemisphaericum
(Bull.) Hornem.
10' Sporocarps ± spherical, occasionally with an umbilicate base. 11
11   (10) Sporocarps rose. Spores with distinct, scattered warts. D. carneum Nann.-Bremek.
11' Sporocarps white, beige or greyish. Spores closely and finely warted. 12
12   (11) Columella hemispherical, ca. 1/3 to 1/2 of the sporocarp diam. Spores 9-12 µm in diam. Stalk short and thick, often hidden in the basal umbilcus of the sporocarp. D. umbilicatum Pers.
12' Columella spherical, less than 1/3 of the sporocarp diam. Spores 8-9 µm in diam. The length of the stalk approximately as the sporocarp diam. D. montanum (Meyl.) Meyl.
13   (1) Sporocarps with a long, stout stalk, spherical to ovoid. Spores with remarkably scattered warts. D. floriforme (Bull.) Pers.
13' Sporocarps sessile or shortly stalked, mostly ± spherical. Spores finely warted. 14
14   (13) The stalk short and stout, often hidden in the basal umbilicus of the sporocarp, occasionally almost lacking. Columella hemispherical, large, up to half the sporocarp diam. D. radiatum (L. ) Morgan
14' Stalk missing, or if it is present then delicate. Columella small, less than 1/3 the sporocarp diam. or missing. 15
15   (14) Sporocarps with a short, delicate stalk or sessile, yellowish brown to reddish brown. The middle perial layer with crystalline lime. Lepidoderma trevelyanii (Grev.) Poulain & Mar.Mey.
15' Sporocarps sessile, purple-brow to dark reddish brown. Lime granular. D. asteroides
(Lister & G. Lister) G. Lister