Key to the species of the genus Stemonitis 1. Columella ending with expansions ....................................................................................................................................................2 - Columella ending without expansions ...............................................................................................................................................6 2. Spores reticulate ............................................................................................................................................... S. amphorocolumella - Spores not reticulate ..........................................................................................................................................................................3 3. Columella ending with membranous cup-like expansions ........................................................................................... S. flavogenita - Columella ending with widened expansion at the apex ....................................................................................................................4 4. Capillitium without free ends .................................................................................................................................... S. sichuanensis - Capillitium with free ends .................................................................................................................................................................5 5. Spores 9–11 µm diam., spinulose ......................................................................................................................... S. capillitionodosa - Spores, 7–8 µm diam., large warts and small warts ......................................................................................... S. pseudoflavogenita 6. Spores reticulate ................................................................................................................................................................................7 - Spores not reticulate ........................................................................................................................................................................11 7. Reticulum with large or medium meshes on spores ..........................................................................................................................8 - Reticulum with small meshes on spores ............................................................................................................................................9 8. Reticulum black, with 2–4 meshes across the spore. Spores dark brown in mass, red-brown in transmitted light, 8–9 µm diam. ... ..................................................................................................................................................................................... S. inconspicua - Reticulum with 6 meshes across the spore. Spores bright lilac-brown in mass, pale lilac-brown, light reddish or pinkish brown in transmitted light, 6–8 µm diam. .................................................................................................................................. S. virginiensis 9. Reticulum with 8–11 meshes across the spore. Spores reddish-brown to dark brown in mass, brownish-grey in transmitted light, 8–9 µm diam. .................................................................................................................................................................... S. marjana - Reticulum with 6–9 meshes across the spore ..................................................................................................................................10 10. Spores gray-purple, brown-purple in mass, purple-brown in transmitted light, 7–9 µm diam., sporocarps 6–20 mm total height ... ................................................................................................................................................................................................ S. fusca - Spores dark brown in mass, purple gray in transmitted light, 8–9 µm diam., sporocarps 3 mm total height .................. S. foliicola 11. Spores in clusters ................................................................................................................................................................ S. uvifera - Spores free .......................................................................................................................................................................................12 12. Sporocarps large or medium 7–20 µm ............................................................................................................................................13 - Sporocarps small up to 5 (7) µm. ....................................................................................................................................................16 13. Sporocarps light brown, spores 5.0–7.5 µm diam., with very fine pale warts seen by oil-immersion .............................. S. axifera - Sporocarps dark brown to black ......................................................................................................................................................14 14. Capillitium without internal net, surface net with large meshes 60–275 µm diam. ................................................... S. rhizoideipes - Capillitium with internal and surface net ........................................................................................................................................15 15. Surface net irregular, many expansions in the axils of the surface net capillitium ............................................................... S. plana - Surface net without many expansions in the axils of the surface net capillitium ........................................................... S. splendens 16. Sporocarps light brown ....................................................................................................................................................................17 - Sporocarps dark brown to black ......................................................................................................................................................19 17. Stalk long, 1/3–1/2 of the total height ................................................................................................................................ S. pallida - Stalk short, 1/5 of the total height ....................................................................................................................................................18 18. Sporocarps gregariously tufted on a common hypothallus. Hypothallus a rather thick, dark red brown membrane, darker at the stalk bases .......................................................................................................................................................................... S. graciliformis - Sporocarps in groups. Hypothallus membranous, inconspicuous .................................................................................. S. herbatica 19. Spores small, up to 7 µm diam. ........................................................................................................................................ S. farrensis - Spores large 8.5–12.5 µm diam. ......................................................................................................................................................20 20. Spore-mass black. Spores with long warts, up to 0.8 µm. ...................................................................................... S. mussooriensis - Spore-mass pale brown. Spores with short warts ............................................................................................................................21 21. Capillitium smooth, not bearing spines internal. Internal net with 3–4 meshes across the radius ..................... S. mediterraneensis - Capillitium lax, with short thick, protrusions on the outside, rather wide, flat to rounded, all the axils rounded and with membranous expansions. Internal net with 1–2 meshes across the radius ............................................................................................... S. laxifila

Published as part of Vlasenko, Anastasia V., Moreno, Gabriel H. & Vlasenko, Vyacheslav A., 2023, Stemonitis amphorocolumella (Stemonitidaceae, Myxomycetes), a new species from Western Siberia, pp. 59-67 in Phytotaxa 592 (1) on pages 64-65, DOI: 10.11646/phytotaxa.592.1.5, http://zenodo.org/record/7835677