Dicranum majus

Turner
Muscol. Hibern. Spic., 59. 1804,.
Treatment appears in FNA Volume 27. Treatment on page 405. Mentioned on page 399, 403.

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.

Discussion

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.

Selected References

None.

Key

1 Leaves falcate-secund, 8-15 mm; margins serrate in the distal half; costa toothed distally on abaxial surface, with a double row of guide cells. Dicranum majus var. majus
1 Leaves erect-patent, 6-8 mm; margins slightly serrulate above to almost entire; costa serrulate to nearly smooth distally on abaxial surface, with an interrupted double row of guide cells Dicranum majus var. orthophyllum