Dicranum laevidens R. S. Williams
Plants in loose to dense tufts, green to yellowish green or brown, glossy. Stems 2.5--7 cm, densely tomentose with reddish brown rhizoids. Leaves straight, erect-spreading, little changed when dry, smooth, (4--)5.5--8(--9) ´ 0.5--1 mm, concave below, tubulose above, from a lanceolate base to a long-acuminate subula, apices acute or sometimes ± blunt; margins entire or slightly serrate in the distal 1/3; laminae 1-stratose; costa percurrent to shortly excurrent, 1/10--1/6 the width of the leaves at base, smooth to slightly rough above on abaxial surface, abaxial ridges lacking, with a row of guide cells, two well-developed stereid bands extending almost to apex, abaxial epidermal layer of cells differentiated, rarely some cells in adaxial epidermal layer enlarged; cell walls between lamina cells not or slightly bulging; leaf cells smooth; alar cells 2-stratose, well-differentiated, not extending to costa; proximal laminal cells elongate, pitted, (16--)36--62(--112) ´ (3--)7--8(--20) µm; distal laminal cells short-rectangular to irregularly angled, pitted, (9--)10--17(--31) ´ (3)7--8(18) µm. Sexual condition pseudomonoicous; dwarf males on rhizoids of female plants; interior perichaetial leaves abruptly acuminate, convolute-sheathing. Seta 2.5--3.5 cm, solitary, rarely 2 per perichaetium, yellow to reddish yellow. Capsule 2--3.5 mm, arcuate, inclined, furrowed when dry, light to dark brown; operculum 1.5--2.8 mm. Spores 14--22 µm.
Capsules mature in summer. Fens, wet meadows, willow thickets, or humus or soil on or around rocks at lake margins; occasionally drier habitats, such as beach ridges; 10--2300 m; sw Greenland; Alta., B.C., Man., Nfld., Nun., Ont., Que., Sask.(Bellolio-Trucco and Ireland 1990), Yukon; Alaska, Colo.(Peterson 1979), Mont. (Eversman and Sharp 1980), Utah (Flowers 1973), Wyo.; Europe; Asia.
This is an Arctic-alpine species known principally by the 4--9 mm, straight, erect-spreading leaves, scarcely changed when dry, concave below, tubulose above, narrowed from a lanceolate base to a long-acuminate subula ending in an acute to ± blunt apex; the elongate, pitted cells throughout the leaf; and the costa that is smooth to somewhat rough above on the abaxial surface. Dicranum angustum Lindberg, often considered distinct because of its blunt leaf apices, is considered a synonym after examination of its type from Europe (see discussion by G. Bellolio-Trucco and R. R. Ireland 1990).