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 proximally, 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. nw, ne North America, Europe, Asia.
Varieties ca. 12 (2 in the flora). Dicranum majus is the only North American species of the genus 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.
Plants: in loose tufts, green to light green, glossy. Leaves: falcate-secund, flexuose, 8–11.5(–15) mm; margins serrate in distal half; costa percurrent to shortly excurrent, toothed distally on abaxial surface, with a double row of guide cells. Phenology: Capsules mature spring.
Humus, soil, soil over rock, and rotten wood in coniferous woods, bogs, and tundra. 0-1500 m. Greenland, Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.W.T., N.S., Nunavut, Ont., P.E.I., Que., Yukon, Alaska, Maine, Mass., R.I., Wash., Europe, Asia.
Variety majus is known by its glossy, long (8–15 mm), falcate-secund leaves with serrate margins in the distal half, by its costae with two rows of guide cells (seen in cross section), the abaxial surface toothed and not ridged distally, and by its aggregate setae (2–5 per perichaetium).