Bryum alpinum Hudson ex Withering, Syst. Arr. Brit. Pl. ed. 4, 3: 824. 1801

Plants medium-sized, dark red to red-green, rarely entirely green, sometimes black with age. Stems 0.5-2(-3) cm, somewhat julaceous, with metallic sheen, older stem sometimes densely radiculose. rigid, strongly imbricate when dry, red to red-green, sometimes green, broadly lanceolate to narrowly ovate or lingulate, occasionally narrowly triangular, weakly concave, 1-3 mm; base not decurrent; margins revolute proximally, plane distally, entire to finely serrulate distally, limbidium absent; apex acute, not cucullate; costa reddish, percurrent to short-excurrent, awn stout; basal laminal cells occasionally pigmented, in 1 row; proximal cells abruptly quadrate to short-rectangular, 1-2(-3):1; medial and distal cells elongate-hexagonal to vermicular, (50-)60-80 × (8-)10- 12 µm, 6-8:1, walls strongly incrassate, parallel to costa. Specialized asexual reproduction rare, by rhizoidal tubers on rhizoids arising from leaf axils, red to red-brown, 100-300 µm. Seta ± straight, red, red-brown, or purple. Capsule inclined to nutant, red-purple, pyriform, 3-5 mm, neck short. Spores 10-15 µm, smooth to papillose, yellowish.

Capsules mature spring-summer. Moist acidic rock, soil over rock; low to high elevations (0-2500 m); Greenland; Nfld. and Labr.; Alaska, Calif., Colo., Ill., N.H.; w, n Eurasia; n Africa.

Imbribryum alpinum is a relatively rare boreal-temperate species characterized by narrow, shiny-metallic red leaves and incrassate, elongate distal laminal cells; capsules are rare. Most reddish plants similar to this species in the western United States do not conform well to this set of characters. Instead, most collections have red, broadly ovate leaves, shorter distal laminal cells, and short-excurrent costae. This material cannot be referred to either I. alpinum or I. muehlenbeckii, and apparently represents an undescribed species. Reports from southern Africa need to be verified as other red-colored species occur in the Southern Hemisphere. The Alaska collection is from St. Lawrence Island.