Dicranum drummondii C. Müller 1848

Dicranum drummondii represents an interesting complex with different expressions in plant size, color, thickness of leaf margins, and alar cells. Chinese collections of this species and the types of Dicranum caesium, D. diplospiniferum, D. thelinotum, and D. truncicola all fall within these expressions. This complex represents a single, variable species.

Dicranum drummondii, primarily an Eurasian species, was for years confused with the endemic North American species Dicranum ontariense W. L. Peterson (see discussion under 9. D. ontariense). It was only recently (August 2000) that W. B. Schofield, S. S. Talbot, and S. L. Talbot made the first and only collection of the species, which was sterile, from Attu Island in the Aleutian Islands. The species is best recognized by its robust size, stems 5-11 cm, its leaves yellowish green to yellowish brown, undulate or rugose, erect and compressed, becoming flexuose at the tips when dry, concave below and keeled above, with an oblong-ovate base, becoming long-acuminate at apex, margins strongly toothed above, and costa percurrent to shortly excurrent, without lamellae. Microscopically, distinguishing characters are the leaves in the distal part with round, oblong, somewhat rectangular cells with few pits, cells smooth or prorate on abaxial surface, in cross section the lamina with a few scattered 2-stratose cells, cells walls between the lamina cells not bulging, and costa with a few cells differentiated on the adaxial epidermal surface.

Plants usually robust, up to 15 cm high, yellowish green to yellowish brown, shiny, in loose tufts. Stems erect, simple or branched, densely radiculose below. Leaves small and distant below, becoming larger and crowded above, in multi-rows, erect or flexuose when dry, falcate-secund when moist, lanceolate, up to 12 mm × 1.5 mm, contracted at base, gradually narrowed from an oblong-ovate base to a long, keeled or subulate acumen, often distinctly undulate above; margins plane, entire below, irregularly double-toothed, bistratose above; costa slender, occupying ca. 1/10 the leaf base width, shortly excurrent, papillose or sharply serrate at back above, without lamellae; upper cells quadrate to short-rectangular, thick-walled, not porose, papillose on the leaf dorsal surface; basal cells elongate, rectangular, thick-walled, porose; alar cells quadrate, somewhat inflated, multi-stratose (4–5 layered), brownish, not extending to the costa. Dioicous. Male plants dwarfed. Perichaetial leaves convolute-sheathing at the base, abruptly subulate. Setae slender, straight, 3–5 cm long, yellowish, 2–3 per perichaetium; capsules short-cylindric, curved, inclined to horizontal, striate when dry, yellowish brown; opercula conic-rostrate; peristome teeth lanceolate, divided unequally to the middle, reddish brown. Spores 14–18 µm in diameter, brownish.

Plants in loose tufts, yellowish green to yellowish brown below, shiny to dull. Stems 5-11 cm, densely tomentose below with reddish brown rhizoids. Leaves erect and compressed to somewhat flexuose, curled to flexuose at apices when dry, undulate or rugose, (7-)8-10(-12) × 1.5-2 mm, concave below, keeled above, from an oblong-ovate base to a long-acuminate apex; margins incurved to tubulose below, plane and strongly serrate above; laminae 1-stratose below, sometimes a few scattered 2-stratose regions above; costa percurrent to shortly excurrent, ¹/10-¹/6 the width of leaves at base, papillose to serrate above on abaxial surface, without lamellae, with a row of guide cells, two stereid bands above and below extending to apex, adaxial epidermal layer of cells with a few cells slightly larger than the stereids differentiated, the abaxial layer completely differentiated with cells slightly larger than the stereids; cell walls between lamina cells not bulging; leaf cells smooth or a few cells prorate on abaxial surface; alar cells 2-stratose, differentiated, extending to costa; proximal laminal cells irregularly rectangular, often narrowed at ends, narrow and elongate on margins, pitted, (67-)82-98(-112) × (5-)6-8(-9) µm; distal laminal cells round, oblong, somewhat rectangular, with a few pits (9-)13-19(-30) × (3-)6-9(-12) µm. Sterile, no sex organs seen. [Sexual condition pseudomonoicous, male plants on leaves of female plants. Interior perichaetial leaves abruptly subulate, convolute-sheathing. Seta 3-5 cm, 2-3 per perichaetium, sometimes solitary, yellowish. Capsule 2.5-3.5 mm, arcuate, inclined to horizontal, striate when dry, yellowish brown; operculum 2.3-3 mm. Spores 14-18 µm.]

Distribution: China, Korea, Japan, Russia, and Europe.

Habitat: on soil and rocks in mixed hardwood conifer forests.

Dicranum caesium Mitt., Trans. Linn. Soc. London, Bot. sér. 2, 3: 155. 1891, syn. nov. Type. Japan: Faurie 301 (holotype NY; isotype H). Dicranum diplospiniferum C. Gao & Z.-W. Ao, Bull. Bot. Lab. N.-E. Forest. Inst., Harbin 7: 99. 1980, syn. nov. Type. China: Xizang, Mi-lin Co., S.-K. Chen 4876 (holotype KUN). Dicranum elatum Lindb., Bot. Not. 1865: 78. 1865, nom. illeg. incl. spec. prior. Dicranum perfalcatum Broth., Akad. Wiss. Wien, Sitzungsber., Math.-Naturwiss. Kl. Abt. 1, 131: 209. 1923, hom. illeg. Type. China: Sichuan (Setschwan), Handel-Mazzetti 1413 (holotype H). Dicranum robustum Blytt ex Bruch & Schimp. in B.S.G., Bryol. Eur. 1: 147. 1847. Dicranum thelinotum C. Müll., Nuovo Giorn. Bot. Ital. n.s. 3: 98. 1896, syn. nov. Type. China: Shaanxi, Taibai Shan (Mt.), Giraldi 942 (holotype B, probably destroyed; isotype H). Dicranum truncicola Broth., Akad. Wiss. Wien, Sitzungsber., Math.-Naturwiss. Kl. Abt. 1, 133: 561. 1924, syn. nov. Type. China: Sichuan, Yan-yuan (Yeng-yuen) Co., Handel-Mazzetti 5731 (holotype H).

Dicranum elatum Lindberg; D. robustum Bruch & Schimper