Plants: medium-sized, not in tufts, pale yellow-green to golden green. Stems: 2â10 cm, yellowish to pale green, creeping, not complanate-foliate, regularly and closely pinnate to plumose, branches 0.2â1.5 cm; hyalodermis present, central strand weak or absent; pseudoparaphyllia foliose. Stem: leaves circinate-secund, ovate-lanceolate, gradually tapering to insertion, gradually narrowed to apex, 1.5â2.8 à 0.4â0.6 mm; base not decurrent; margins plane, sinuate proximally, serrate toward apex; apex narrowly acuminate; costa double, short, indistinct, less than 1/3 leaf length; alar region slightly differentiated, of 3 or 4 cells at extreme basal angles; basal laminal cells shorter, broader than medial cells, not strongly pigmented, walls pitted; medial cells 50â80(â90) à 3â4 µm. Sexual: condition dioicous; inner perichaetial leaves lanceolate, weakly or not plicate, margins slightly toothed or entire near apex. Seta: red-brown, 2.5â3 cm. Capsule: erect to suberect, light brown, cylindric, 3â5 mm; annulus 1â3-seriate; operculum conic or rostellate; endostome cilia unknown. Phenology: Capsules mature MayâJun. Habitat: Epiphytic on living trees, cliffs, vertical rock faces, decaying logs, terrestrial Elevation: low to moderate elevations (0-1500 m) Distribution: B.C., N.W.T., Nunavut, Yukon, Alaska, Calif., Idaho, Mont., Oreg., Wash., e Asia.
Discussion: Specimens of Hypnum subimponens from Arctic regions are problematic; in fact, any specimens from horizontal surfaces can be difficult to place accurately. Sporophytes, produced in spring, are frequent only on vertical surfaces and then often abundant. Unlike similar species in western North America, H. subimponens produces cylindric, erect capsules (slightly curved below the mouth when mature). Hypnum lindbergii has falcate-secund leaves, while those in H. subimponens are circinate-secund to strongly hamate. Key traits of the stem leaves separate H. subimponens from H. hamulosum, and the former is usually more than twice the size of the latter. See also discussions of 3. H. callichroum, 11. H. holmenii, and 16. H. plicatulum. Plants of H. subimponens have branches 0.5â1 mm wide; the alar cells are slightly bulging, hyaline, and thin-walled.