Tropicos | Name - !Didymodon nigrescens (Mitt.) K. Saito

Cent. Amer. Moss > Pottiaceae > Didymodon > Didymodon nigrescens

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!Didymodon nigrescens (Mitt.) K. Saito

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Project Name Data (Last Modified On 2/15/2011)

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Project data (Last Modified On 2/15/2011)

Discussion:

Didymodon nigrescens has a distinctive red-brown color and stiffly erect to imbricate, scarcely contorted leaves that are usually broadly rounded to cucullate at the apex. Its leaf cells are very thick-walled and the upper ones are bulging mammillose. The species lacks a stem central strand, and although costal stereids are usually absent, the guide cells can be somewhat enlarged making the cells above and below them substereid-like. Other distinctive features of the species include broad leaf decurrencies consisting of enlarged, somewhat inflated cells, exceedingly thick-walled inner, basal leaf cells, and long perichaetial leaves.

Didymodon acutus, D. icmadophilus and D. vinealis have similar leaf shapes, however they differ from D. nigrescens in having dark- to yellow-green, incurved-twisted leaves, a stem central strand and at least dorsal stereids in their costae. Didymodon acutus and D. icmadophilus also differ from D. nigrescens in having long-excurrent costae. Didymodon vinealis like D. nigrescens has percurrent costae and leaf decurrencies; it further differs however in having pluripapillose upper leaf cells.

Illustrations: Bartram (1949, Fig. 56 C–G as B. brunneola); Saito (1975, Fig. 52); Lawton and Hermann (1972, Figs. 1–15). Figure 27.

Habitat: On limestone; 3100–3500 m.

Distribution in Central America: GUATEMALA. Huehuetenango: Williams et al. 41093 (FH, MO).

World Range: Subarctic America, Northwestern U.S.A.; Central America; China, Eastern Asia; Indian Subcontinent.

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Didymodon nigrescens (Mitt.) Saito, J. Hattori Bot. Lab. 39: 510. 1975.

Barbula nigrescens Mitt., J. Proc. Linn. Soc., Bot. Suppl. 1: 36. 1859. Protologue: Sikkim. In Himalayae reg. temp., Sikkim, J. D. Hooker (No. 169). Kumaon, Stachey et Winterbottom.

Barbula brunneola C. Müll., Bull. Herb. Boissier 5: 196. 1897. Protologue: Guatemala. Chemal, Sept. 1876 (localitas verosimiliter alpina!), cum Bryo (Sclerodictyo) perappresso. [Bernoulli & Cario].

Plants small, dull, reddish brown, in loose or dense tufts, to 30 mm high. Stems red, erect, irregularly, branched, hyalodermis present, central strand absent; rhizoids sparse, at base of stems or scattered throughout. Axillary hairs 4–6 cells long, basal cell brown. Leaves 1–2 mm long, ovate-lanceolate to linear-lanceolate from an ovate base, spreading at base, crowded on stems, erect-imbricate to appressed when dry, erect-spreading when wet, plane along the costa on ventral surface; apices broadly acute to rounded-obtuse or cucullate, decurrent; lamina unistratose, margins entire, recurved to above midleaf; costa subpercurrent to percurrent, surface ventral cells quadrate, guide cells poorly-developed, dorsal and ventral stereid bands absent or present as substereids, dorsal surface cell layer somewhat enlarged; upper and median cells rounded, rounded-quadrate or oblate, 4–10 x 4–10 μm, thick-walled, bulging mammillose, basal cells short-rectangular to rhomboidal, thick-walled, smooth, 10–30 x 6 μm, alar cells not differentiated, decurrent cells enlarged to inflated, quadrate to rectangular, 20–44 x 10–12 μm. Dioicous. Perichaetia terminal; perigonia not seen; perichaetial leaves erect, longer than vegetative leaves, to 3 mm long. Setae smooth, twisted clock-wise, 5–8 mm long, red. Capsules long-cylindrical, erect, 1.5–2.0 mm long, smooth; exothecial cells rectangular, firm-walled; stomata in neck; opercula erect, long-rostrate, 1 mm long; annuli moderately developed, adhering to the capsule; peristome reddish yellow, basal membrane low, teeth twisted, to 1 mm long. Spores 8–10 μm, smooth. Calyptrae cucullate, to 2 mm long.