Linnaea 38: 220. 1874.
Plants small to large, in dense or loose tufts, light to deep green, sometimes yellowish, brownish, or rarely brownish red with age. Stems creeping, ascending, or arching, not attenuate, loosely to densely terete- or rarely complanate-foliate, julaceous or not, irregularly to sometimes fairly regularly pinnate, branches somewhat more densely foliate than stem, terete- to complanate-foliate; central strand present; pseudoparaphyllia acute; axillary hairs of 2–3(–5) cells. Stem leaves erect to patent and reflexed, loosely arranged to closely imbricate, broadly ovate, ovate-lanceolate, or deltoid, slightly to strongly concave, indistinctly plicate to not plicate; base broadly or narrowly short- or long-decurrent; margins coarsely serrate to subentire; apex gradually or abruptly tapered, acuminate, acute, or apiculate; costa reaching mid leaf to percurrent, strong, weak, or broad proximally and narrowed distally, terminal abaxial spine small or absent; alar cells subquadrate to short-rectangular, enlarged or not, walls thin or moderately thick; laminal cells slightly elongate (3–4:1) to linear (10–20:1), smooth (occasionally prorate abaxially in S. starkei), walls thin to moderately thick; basal juxtacostal cells undifferentiated, or broader and region pellucid, or slightly broader, walls moderately thick, and region opaque across base. Branch leaves smaller, narrower; costal terminal spine more often present; laminal cells not prorate. Sexual condition autoicous (dioicous in S. hylotapetum and S. latifolium); perichaetial leaves reflexed. Seta red-brown or sometimes cherry red, rough or sometimes weakly so to almost smooth. Capsule inclined, horizontal, or pendent, dark red-brown, elongate to short-ovate, straight or curved; annulus separating by fragments; operculum conic to long-conic, occasionally short-rostrate; peristome xerocastique, perfect. Calyptra naked. Spores 9–20 µm.
Nearly worldwide, boreal and temperate zones, alpine to middle elevations in the tropics.
Species ca. 30 (11 in the flora).
Sciuro-hypnum was segregated from Brachythecium by M. S. Ignatov and S. Huttunen (2002). Previously, species of Sciuro-hypnum were placed in Brachythecium in two sections: sect. Reflexa Brotherus and sect. Plumosa De Notaris (V. F. Brotherus 1924–1925). Sciuro-hypnum differs from Brachythecium in the mostly small plant size, the almost always autoicous sexual condition (except S. hylotapetum and S. latifolium), and rough setae. Among species of Brachythecium, the combination of autoicous sexual condition and a rough seta is uncommon in North America and is known only in B. bolanderi, B. campestre, and B. rutabulum. The stem leaves are occasionally twisted or falcate-secund. Immature capsules are sometimes strongly patent to circinate with the operculum turned upward.
|1||Costae to 80% leaf length to percurrent||> 2|
|1||Costae to 20-80% leaf length||> 6|
|2||Basal laminal cells relatively small, quadrate, subquadrate, or short-ovate, regions opaque across base; alar cells similar to juxtacostal cells||> 3|
|2||Basal juxtacostal cells somewhat wider and shorter than laminal cells, not clearly differentiated; alar cells ± enlarged, usually pellucid, sometimes appearing opaque due to collapsed cytoplasm, in this case opaque regions restricted to leaf corners, reaching from margin 50% distance to costa||> 4|
|3||Leaves straight; widespread.||Sciuro-hypnum populeum|
|3||Leaves falcate-secund to reflexed; Alaska.||Sciuro-hypnum uncinifolium|
|4||Laminal cells 3-6:1.||Sciuro-hypnum reflexum|
|4||Laminal cells (6-)7-15:1||> 5|
|5||Plants soft; stems irregularly or rarely regularly pinnate; stem leaves appressed to stem at bases; apices long-acuminate; branch leaf distal laminal cells smooth.||Sciuro-hypnum reflexum|
|5||Plants rigid; stems regularly pinnate, at least in part; stem leaves erect- to wide-spreading; apices gradually tapered or rarely short-acuminate; branch leaf distal laminal cells prorate.||Sciuro-hypnum starkei|
|6||Plants large, whitish to pale yellowish; stem leaves 2.2-3.7 × 1.3-2 mm; sexual condition dioicous; montane forests of w North America.||Sciuro-hypnum hylotapetum|
|6||Plants small to moderately large, green, yellow, or brownish, occasionally reddish; stem leaves no larger than 1.4-2.4 × 0.9-1.5 mm; sexual condition usually autoicous; widespread||> 7|
|7||Alar cell walls moderately thick, regions not pellucid||> 8|
|7||Alar cell walls thin, regions pellucid||> 10|
|8||Leaves ovate-lanceolate to ovate.||Sciuro-hypnum plumosum|
|8||Leaves ovate or ovate-triangular||> 9|
|9||Leaves 1-1.5(-1.8) × 0.6-0.9(-1.1) mm; apices acute or short-acuminate; bases short-decurrent, inconspicuous; arctic to alpine.||Sciuro-hypnum glaciale|
|9||Leaves (1.2-)1.6-2.2 × (0.5-)0.7-1.1 mm; apices short- to long-acuminate; bases broadly long-decurrent, conspicuous; widespread in mountains of w North America, mainly forest, occasionally alpine.||Sciuro-hypnum oedipodium|
|10||Leaf margins entire or minutely serrulate in acumen; plants light green to yellowish; sexual condition dioicous.||Sciuro-hypnum latifolium|
|10||Leaf margins serrate to subentire; plants usually darker green; sexual condition autoicous||> 11|
|11||Leaves imbricate, strongly concave, broadly ovate to broadly oblong; apices broadly acute, often short-apiculate; rare, Arctic Alaska.||Sciuro-hypnum ornellanum|
|11||Leaves loosely arranged, slightly concave, ovate or ovate-triangular; apices gradually acuminate to narrowly acute; widespread in boreal and hemiboreal forests of e North America, rare in Rocky Mountains.||Sciuro-hypnum curtum|