Polytrichaceae. Genus Atrichum
1. Dioicous; lamellae 4-11 cells high; stems 1-2 (-3) cm long —
— Autoicous or paroicous; lamellae 2-4(-6) cells high; stems (1-)3-5 cm long —
2. Leaves rather soft, ovate-lanceolate; margins weakly serrate; dorsal surface of lamina smooth or with solitary teeth; cells 18-30(-35) µm wide —
3. A. tenellum
Widespread in boreal regions of European Russia, especially in disturbed environments: abandoned fields, along roads, etc. ; rare in other regions. Can be confused with young plants of A. undulatum which often have taller lamellae than adult plants.
— Leaves rigid, lanceolate to linear; margins coarsely serrate; dorsal surface of lamina with teeth in oblique rows; laminal cells 10-18 µm wide —
3. Lamellae 6-10, 6-11 cells high; European Russia and Caucasus —
2. A. angustatum
Sporadic in the Black Sea coastal area of the Caucasus, rare in other parts of the Caucasus and in other western regions of European Russia.
— Lamellae 4(-6), 4-9 cells high; southern part of Russian Far East —
1. A. rhystophyllum
Somewhat rare in the Russian Far East. The species has leaves broader than those of A. angustatum and most leaves have only four rows of lamellae. Small leaf cells separate it from all other Far Eastern species of the genus.
4. Sporophytes 1(-2) per perichaetium, terminal; setae thick, red; capsules inclined, curved; exothecial cells length/width ratio 1. 5:1, not in conspicuous vertical rows; mostly autoicous —
4. A. undulatum
Common in broad-leaved and southern boreal forests of European Russia and Russian Far East where it grows on soil banks (in a broad range of habitats, including forests), rare in Siberia.
— Sporophytes (1-)2-3 per perichaetium, terminal or lateral; setae thin, yellow; capsules suberect to almost straight; exothecial cells length/width ratio 2:1, in conspicuous vertical rows; mostly paroicous —
5. A. flavisetum
Sporadic in boreal regions of European Russia, more common in south Siberian and Far Eastern taiga. This species is quite distinct from the previous one in European Russia and Siberia, but in the Russian Far East the distinction is not apparent, likely due to the occurrence of another cryptic species.