Bryaceae. Genus Plagiobryum

1. Plants red to reddish brown; innovations not julaceous, not forming main part of tuft; innovation leaves erect to erect-spreading, narrowly ovate-triangular, margins recurved 1. P. demissum

This arctic-alpine species is rare in Russia and occurs mostly in the relatively dry tundra in Siberia, both in Arctic and high mountains. It is similar to other Plagiobryum species in having curved capsules with strongly elongate apophyses, but its stem and innovation leaves are narrowly ovate-triangular with recurved margins rather than broadly ovate to round with usually plane margins.

Plants green, pale-green, brownish, whitish or silvery, at times with a pearl luster or green-rose sheen due to large-sized leaf cells; innovations often julaceous, usually forming main part of tuft; innovation leaves imbricate, broadly ovate to round, margins usually plane, rarely recurved 2

2. Ñapsules straight with transverse mouths; exostome about half endostome length 4. P. japonicum

This species is found in Far Eastern Russia. It is somewhat similar to P. zieri in having long julaceous innovations. But differs fromB. zieri in having more distinctly reflexed innovation leaf apices and strongly excurrent costae that give the innovations a more“setaceous” aspect that is especially pronounced in plants from drier habitats.However, the exostome of P. japo­nicum like that of P. demissum is shorter than the endostome, while the exostome in P. zieri is equal the endostome. Plagiobryum demissum is also similar to P. japonicum in having spores that remain as tetrads, but its non-julaceous innovations, narrowly ovate-triangular leaves with recurved margins and strongly curved capsules makes it difficult to confused them.

Capsules somewhat curved with oblique mouths; exostome as long as endostome 3

3. Plants pale-green to silvery, with a strong pearl luster or green-rose sheen; julaceous innovation leaves ovate-rounded, strongly concave, broadly tapered above, margins plane; fertile stem leaves ovate-elliptic, moderately concave, gradually tapered above, margins plane; capsule necks longer than urns 3. P. zieri

This widespread Holarctic species is moderately rare on wet rocks (often close to waterfalls) in the mountains throughout Russia, especially in areas with calcareous bedrock. Its tumid plants are similar to those of Bryum argenteum in aspect, but differ in having a curious pearl luster or green-rose sheen that make it immediately recognizable. Plants of P. japonicum have a similar color, but that species differs from P. zieri in having shorter exostome teeth as well as other features noted in the key.

Plants pale-green to brownish, dull; innovation and fertile shoot leaves more or less similar, ovate-elliptic, moderately concave, gradually tapered above, margins moderately recurved; capsule necks equal to or shorter than urns 2. P. hultenii

Plagiobryum hultenii is known from the Russian Far East and Japan. It differs from all other species in the genus in having only pale-green or brownish plants. It is similar to P. demissum in having recurved leaf margins and no conspicuous stem/branch innovations. But, differs in having larger leaves (1.3–3.00.4–1.1 vs. 0.8–1.50.2–0.4(–0.5) mm) that are ovate-elliptic rather than ovate-triangular.