Black Didymodon Moss

The specimens cited as Didymodon nigrescens from the Firth River Basin by W. C. Steere (1978), determined by R. H. Zander, are actually Didymodon subandreaeoides. The distinguishing characters of D. nigrescens are the blackish coloration when dry (red in KOH), thin costa and distal laminal margins minutely crenulate by the small, bulging marginal cells. This and the following two species appear to be closely related by the rather distinctive crenulation of the leaf apices. Didymodon asperifolius is similar but may be distinguished by its longer leaves, straight or reflexed to strongly recurved when wet, distal margins recurved and smooth, distal laminal cells larger, 10-13 µm wide, epapillose or papillae simple, costa usually rather wide.

Plants small to medium-sized, 10–20 mm high, dark green to dark reddish brown, in cushions or dense tufts. Stems erect, often branched; central strand absent. Leaves appressed or somewhat involute when dry, erect-spreading when moist, broadly ovate- to shortly ovate-lanceolate, 1.3–1.6 mm × 0.3–0.5 mm, narrowly obtuse to blunt at the apex; margins entire, distinctly revolute; costa stout, dark brown, percurrent or ending just below the apex; upper leaf cells rounded hexagonal, 6–12 µm × 8–12 µm, thick-walled, with blunt large papillae; basal cells rectangular, 12–24 µm × 8–14 µm, thick-walled, smooth or sometimes with single papilla. Dioicous. Perichaetial leaves larger than stem leaves. Setae slender, ca. 7 mm long, dark reddish; capsules erect, blackish red, cylindrical, ca. 2.5 mm long; opercula conic-rostrate with a short beak.

Plants usually red- to black-brown, occasionally yellow- or orange-brown at apex. Stems 1.5-2.3 cm, central strand absent or present. Stem leaves appressed when dry, spreading and not keeled when moist, monomorphic, long-ovate to lanceolate, broadly concave adaxially across leaf, usually 0.8-1.7 mm, base weakly differentiated in shape, long-ovate, margins usually broadly recurved to revolute to mid leaf or to near apex, minutely crenulate, apex acute to narrowly acuminate, often weakly cucullate; costa percurrent or ending 2-4 cells below the apex, little tapering, not strongly spurred, without an adaxial pad of cells, adaxial costal cells rectangular, 2 cells wide at mid leaf grading to 4 below, guide cells in 1 layer; basal laminal cells differentiated medially, walls thick, rectangular, not perforated; distal laminal cells in rows, 7-11(-14) µm wide, 1:1 or often longitudinally elongate, papillae apparently absent but visible in section as low, flattened to multiplex capitulate lenses, 1-3 per lumen, lumens ovate, walls evenly thickened and weakly convex on both sides of lamina, 1-stratose. Specialized asexual reproduction absent. Seta 0.7-0.9 cm. Capsule 1.5-2.8 mm; peristome teeth 32, linear, straight to twisted 1.5 times, 100-600 µm. Spores 9-13 µm. Distal laminal KOH reaction red.

Distribution: China, India, Japan, and North America.

Habitat: on calcareous rocks or cliffs in montane forests or subalpine grasslands.

Andreaea yuennanenis Broth., Symb. Sin. 4: 9. 1929. Type. China: Yunnan, Zhong-dian (Chungtien) Co., Handel-Mazzetti 6952 (holotype H). Barbula subrivicola P.-C. Chen, Hedwigia 80: 213. 35 f. 7–13. 1941. Type. China: Sichuan (Setschwan), Yan-yuan (Yenyuen) Co., Handel-Mazzetti 5538 (holotype H). Barbula subrivicola var. densifolia P.-C. Chen, Hedwigia 80: 215. 1941. Type. China: Sichuan (Setschwan), between Yalung and Tschahung, Handel-Mazzetti 2669 (holotype H).

Barbula nigrescens Mitten, J. Proc. Linn. Soc., Bot., suppl. 1: 36. 1859; B. rufofusca E. Lawton & F. J. Hermann