Polytrichaceae. Genus Pogonatum

1. Stems short, less than 2 mm long, with 4-8 leaves appressed when dry; leaves composed mostly of sheathing base with tapered awn; lamellae absent; plants scattered on deep bluish-green, persistent protonema; Far East — 1. P. spinulosum

Occurs in the southern part of Russian Far East; it grows on bare soil, commonly along roads, usually in relatively xero-mesic oak forests. Its white calyptrae and/or setae contrast sharply with its dark, blue-green protomena, giving the species a quite peculiar appearance.

—Stems 0.5-10 cm long, with (7-)20-100 spreading or rarely, loosely appressed leaves composed of sheathing base and rather long limb; lamellae present on ventral surface; protonema not persistent in most species (may be persistent in P. aloides); various regions — 2

2. Plants large, leaves to 15(-18) mm long and (1.5-) 2-2.5 mm wide; upper cells of lamellae double; Far East — 9. P. japonicum
This species occurs in the mountains of the southern Russian Far East, both in mainland and islands, reaching Kamchatka to the North; it grows within moss carpet in coniferous forests and in Betula ermanii grassy communities. It differs from other species of Polytri¬chaceae in a large size of plants and the largest leaves crowded in a relatively short part of stem, while in a large-sized Polytrichum species stems are evenly foliate.
—Plants medium-sized, leaves to 3-8(-10) mm long and 0.7-1.3 mm wide; upper cells of lamellae single; various regions — 3

3. Leaves rather soft, contorted when dry; lamellae 3-4 cells high; leaf margin bistratose; Far East — 4. P. contortum

Distribution of the species in Russia is confined to a relatively narrow oceanic zone in the Far East, where it is widespread throughout, north to Kamchatka. Unlike other species of the genus, plants of P. contorum are bright green, without any glaucous color, and soft due to a broad unistratose part of the leaf limb and low lamellae. It occurs both in forests and in disturbed places.

—Leaves rigid, straight to more or less curved when dry; lamellae (4-)5-7 cells high; leaf margin always unistratose; various regions — 4

4. Upper cell of lamellae smooth — 5
—Upper cell of lamellae papillose — 8

5. Upper cell of lamellae ovate, similar to cells below — 6
—Upper cell of lamellae broad and flattened at the top, distinct from cells below— 7

6. Leaves slightly serrulate only near apex, more or less blunt, 3-5 mm long; capsule not or only slightly longer than wide — 2. P. nanum
Rare species in westernmost provinces of European Russia, also known from one locality in the Middle European Russia (where it is likely recently introduced). Small plants with very short capsules separate this species from P. aloides.
—Leaves serrulate almost to the sheathing base, acute to more rarely somewhat blunt, 4-7 mm long; capsule cylindrical, about twice longer than wide — 3. P. aloides

This species in widespread in the Black Sea coastal area in the Caucasus, where it grows at low and middle elevations, on bare soil, often along roads and otherwise disturbed places in deciduous forests. Dark blue-green color and subpersistent bluish protonema allow easy recognition of this species in nature (all other Pogonatum species in that region have light glaucous leaves).

7. Upper cell of lamellae somewhat wider than cells below, distally flat to slightly retuse; Caucasus — 6. P. neesii

The species is likely introduced in the Caucasus, where it is known from several localities along the Black Sea coast. There are numerous botanical gardens and dendro-parks in this area, where many East Asian plants were introduced in 20th century. It is easy to distinguish this species from habitually similar P. urnigerum due to narrower leaves that are somewhat flexuose when dry.

—Upper cell of lamellae conspicuously wider than cells below, distally flat to strongly retuse; Far East — 5. P. inflexum
The species is widespread in Primorsky Territory and southern Kuril Islands, but unknown from other areas. It grows on bare soil on eroded slopes and other naturally disturbed areas, as well as along roads and trails. Similarly to P. neesii, it can be recognized from sympatric species by glaucous color, narrow leaves that are somewhat flexuose when dry.

8. Upper cell of lamellae round, with round lumen and convex distal wall; basal membrane 1/3 of peristome length; seta straight to gently curved — 8. P. urnigerum
The most widespread species of the genus in Russia, occurring from Arctic to temperate zone, both in natural and in man-made habitats. Its differentiation from P. dentatium mainly requires microscopic studies, although when sporophytes are present, their straight seta, not bent distally like in the latter species, allows their easy recognition.
—Upper cell of lamellae oblate, with rectangular lumen and flattened distal wall; basal membrane 1/10-1/5 of peristome length; seta geniculate — 7. P. dentatum

The species is widespread in Asian Russia, while in Europe until recently it was confined to the Arctic and northernmost part of boreal zone, and then it started to spread southward, so its populations in central European Russia can be considered as recent invasions. For separation from P. urnigerum see note under that species.