Key to Danish species of Arcyria F.H. Wigg.

1 Spores 9-12 μm in diam. The capillitium attached only at base of calyculus. Sporocarps rusty red to orange red, fading to pale ochraceous. A. ferruginea Saut.
1' Spores 6-9 μm in diam. 2
2   (1) The capillitium attached only at base of calyculus (can be removed as an entity). 3
2' The capillitium attached at base as well as on the side of the calyculus. 9
3   (2) Sporocarps yellow to ochraceous yellow. Capillitium expanding into cylindrical plume at maturity. A. obvelata (Oeder) Onsberg
3' Sporocarps with reddish colours. 4
4   (3) Sporocarps greyish rose, fading to dull beige. Capillitial net wide-meshed. A. incarnata (Pers. ex J.F. Gmel.) Pers.
4' Sporocarps bright red to copper-coloured, fading to brownish red. 5
5   (4) Sporocarps ± globose or somewhat obovoid. Apical part of peridium long persistent, eventually breaking away in flakes. A. helvetica (Meyl.) Neubert, Nowotny & K. Baumann
5' Sporocarps elongated, ± cylindrical, upright or drooping and entangled. Apical peridium completely evanescent or remaining as a very thin, ± iridescent membrane. 6
6   (5) Sporocarps copper-coloured, entangled. Often with flakes of the thin and ± shining peridium still attached. Capillitium short cylindrical, ornamentation mostly including spiral bands. A. stipata (Schwein.) Lister
6' Sporocarps red. No remnants of peridium except calyculus. The capillitium expanding into lax plume. 7
7   (6) Capillitial ornamentation of spines up to ca. 3 μm long. A. oerstedtii Rostaf.
7' The capillitium with short spines, warts, rings and half-rings or ridges, occasionally with a faint net-ornamentation. 8
8   (7) The capillitium with short spines, warts half-rings and ridges, occasionally with a faint net-ornamentation. Sporocarps red to carmin red. A. affinis Rostaf.
8' Capillitial ornamentation only of rings and half-rings. Sporocarps coral red. A. major (G. Lister) Ing
9   (2) Sporocarps greyish rose to red, fading to beige or reddish brown. 10
9' Sporocarps greyish white to ochraceous, rarely with a greenish tint. 12
10   (9) Sporocarps greyish rose, fading to beige. Capillitium notably fine-meshed, unelastic. A. minuta Buchet
10' Sporocarps orange red to carmin-red, fading to reddish brown. 11
11   (10) Sporocarps usually more than 2 mm high, often in large clusters, carmin-red, more rarely very bright red. A. denudata (L.) Wettst.
11' Sporocarps less than 1.5 mm high, in small groups of up to 10-15, bright orange red. A. insignis Kalchbr. & Cooke
12   (9) Sporocarps ochraceous yellow, spherical to ovoid. Capillitium wide-meshed, with ridges and warts, ornamentation uniform throughout. A. pomiformis (Leers) Rostaf.
12' Sporocarps greyish, occasionally with greenish tint. 13
13   (12) Sporocarps greyish white, grey to greyish ochraceous. Short cylindrical to obovoid. Capillitium fine-meshed, with rather close-set spines, in basal parts almost smooth and with thicker tubules. A. cinerea (Bull.) Pers.
13' Sporocarps pale greyish green, cylindical. The capillitium with scattered spines, occasionally with irregular net- or spiral-ornamentation. A. glauca A. Lister