20. Dicranum groenlandicum Bridel, Muscol. Recent., suppl. 4: 68. 1818.
Plants in dense tufts, light green, glossy. Stems 4.5-10 cm, tomen-tose throughout with brown to red rhizoids. Leaves erect-spreading, erect-appressed when dry, smooth, (2.5-)3-4(-6.5) × 0.3-0.5 mm, from an ovate-lanceolate base to a tubulose subula, narrowly obtuse at apex, rarely acute, sometimes apical leaves of stems julaceous; margins entire; laminae 1-stratose, occasional 2-stratose regions near costa in proximal part of leaf; costa subpercurrent to percurrent, 1/10-1/6 the width of the leaves at base, smooth, abaxial ridges absent, with a row of guide cells, two well developed and thick stereid bands (5-6 cells thick), adaxial epidermal layer of cells not differentiated, the abaxial layer usually with a few cells enlarged; cell walls between lamina cells slightly bulging; leaf cells smooth; alar cells 1- or 2-stratose, well-differentiated, not extending to costa; proximal laminal cells elongate-sinuose, strongly pitted, (36-)54-65(-98) × (2-)5-6(-9) µm; distal laminal cells (11-)17-26(-42) × (2-)5-6(-12) µm. Sexual condition dioicous; male plants as large as females; interior perichaetial leaves abruptly short-acuminate, convolute-sheathing. Seta 1.5-2 cm, solitary, yellow to reddish yellow. Capsule 1.5-2 mm, nearly straight and erect to slightly arcuate, ± striate when dry, yellowish brown; operculum 1-1.7 mm. Spores 14-19 µm.
Capsules mature in summer. Arctic or alpine tundra, soil, humus or rocks, sometimes in bogs and fens; 10-3800 m; Greenland; Alta., B.C., Man., Nfld. and Labr. (Nfld.), N.W.T., Nunavut, Ont., Que., Yukon; Alaska, Colo., N.Y.; Europe; Asia.
Dicranum groenlandicum is sometimes not very distinct, often being difficult to separate from its nearest relative, 19. D. elongatum. For distinctions see the discussion under that species.