Dicranum majus Turner, Muscol. Hibern. Spic. 58. 1804.
Plants in loose tufts, green to light green, glossy to somewhat dull. Stems 3--16 cm, naked or with a few whitish rhizoids, rarely moderately tomentose, rhizoids(micronemata) in rows above each leaf. Leaves somewhat sparse, falcate-secund or erect-patent, flexuose or straight, little changed when dry, usually smooth, (6--)8--11.5(--15) ´ 1--2 mm, concave below, tubulose above, from a lanceolate to ovate-lanceolate base, gradually narrowed to a long, falcate-secund or straight, acute apex; margins serrate in the distal half, sometimes slightly serrulate above to almost entire; laminae 1-stratose or with few 2-stratose regions on or near the margins; costa percurrent to shortly excurrent, 1/12--1/7 the width of the leaves at base, toothed distally or serrulate to nearly smooth on abaxial surface, with a double row of guide cells that is sometimes interrupted, two stereid bands extending to apex, adaxial epidermal layer of cells with some cells differentiated, the abaxial layer completely differentiated; cell walls between lamina cells not bulging; leaf cells smooth or abaxially prorate or toothed above; alar cells 2-stratose or multistratose, well-differentiated, not extending to costa; proximal laminal cells elongate, pitted, (42--)71--112(--140) ´ (5--)9--10(--15) µm; distal laminal cells shorter, linear to oval, pitted, (42--)47--61(--99) ´ (7--)10--11(--17) µm. Sexual condition pseudomonoicous; dwarf males among rhizoids of female plants; interior perichaetial leaves abruptly long-acuminate, convolute-sheathing. Seta 2.5--5 cm, aggregate, 2--5 per perichaetium, rarely solitary, yellow to light brown. Capsule 2--3.5 mm, arcuate, inclined to horizontal, smooth to faintly striate when dry, dark brown or yellowish brown; operculum 2--3 mm. Spores 14--19 µm.
Varieties 2 in the flora.
This is the only North American species of Dicranum with a double row of guide cells. It is a distinctive species with oceanic tendencies and in North America it commonly grows in northern coastal localities on both sides of the continent, occasionally occurring inland in very moist habitats.