Funariaceae. Genus Physcomitrium
1. Capsules hemispheric to broadly cupulate, not constricted below mouth; neck absent or very short and not sharply delimited from urn; spores mature in late summer and autumn —
— Capsules pyriform to obovate, usually constricted below mouth; neck clearly delimited from urn; spores mature in spring and early summer —
2. Exothecial cells isodiametric, collenchymatous; leaves obtuse; setae 2–5 µm long; capsules broadly cupulate, often wider than long after dehiscence —
5. P. sphaericum
This species occurs sporadically in southern Russian Far East and is very rare in other parts of the country. Its rarity may be apparent rather than real and due to its development in late summer and autumn when collecting activity is declining. The presence of conspicuously broad cupulate capsules sharply distinguish it from all other Russian species of the genus.
— Exothecial cells short-rectangular, evenly thick-walled; leaves acute; setae 4–8 µm long; capsules hemispheric to cupulate, equal to or slightly longer than wide after dehiscence —
3. Upper leaves usually spatulate, broadly acute, weakly or not apiculate; costae subpercurrent; upper leaf cells mostly elongate-rhomboidal, 50–100-20–40 mm; leaf margins not bordered, serrate above; annuli with two rows of thick-walled cells —
3. P. eurystomum
This species is more common in the southern regions of the Russian Far East and European Russia. The presence of capsules that are not constricted below the mouth is a critical diagnostic character of the species, but the same feature occasionally is present in poorly developed phenotypes of P. pyriforme. Difficult collections can be distinguished by the number of oblate cell rows below the mouth (2–5 in P. eurystomum, 5–13 in P. pyriforme); spore size (30–45 µm in P. eurystomum, 26–37 µm in P. pyriforme); setae length (4–6 µm in P. eurystomum, 5–8 µm in P. pyriforme), and spore maturation time (mid-summer to autumn in P. eurystomum, spring to early summer in P. pyriforme).
— All leaves ovate-lanceolate, acuminate, strongly mucronate; costae percurrrent or excurrent; upper leaf cells mostly rectangular, 30–50-17–25 mm; leaf margins bordered throughout by 1–2 rows of elongate, narrowed, yellowish cells, crenulate above; annuli with one row of thick-walled cells —
4. P. acuminatum
In Russia this species is known from a single collection from the Caucasus. Many authors consider P. acuminatum a synonym or infraspecific taxon of P. eurystomum, but the Russian collection contrasted sharply with P. eurystomum collections from Russia (see characters in the key) and agrees well with the distinctions made between these taxa in the literature.
4. Capsules broadly obovate, more or less abruptly constricted to necks; capsule necks shorter than urn; widespread species —
2. P. pyriforme
A common species in European Russia, also known from scattered localities in the southern part of West Siberia and a single locality in Yakutia.
— Capsules narrowly pyriform, gradually narrowed to necks; capsule necks equal to or longer than urn; rare species in steppe zone of European Russia —
1. P. arenicola
This is a rare species in the steppe and forest-steppe zones of European Russia. It has narrow capsules that sharply distinguish it from other species of the genus, and somewhat resembles those of Entosthodon hungaricus. However, E. hungaricus differs in its much smaller plant size and in having thick-walled rather than thin-walled exothecial cells.