Didymodon obtusus J. Kou, X.

Kou, Jin, Feng, Chao & Shao, Xiao-Ming, 2018, Didymodon obtusus (Bryophyta, Pottiaceae), a new species from Tibet, China, Phytotaxa 372 (1), pp. 97-103 : 98

Didymodon obtusus J. Kou, X. -M. Shao & C. Feng, sp. nov., Figures 1–2

Diagnosis: Didymodon obtusus differs from the otherwise similar D. rigidulus var. subulatus in its ovate-lanceolate to oblong-lanceolate leaves patent to spreading when moist, obtuse leaf apex, and percurrent costa with 3 layers guide cells at base and without ventral stereids.

Type: — CHINA. Tibet, Nagarzê County, 28°55′4.386′N, 90°21′57.888′E, on rocks, 4581 m, 19 Auguest 2014, Jin Kou & Xiao-Ming Shao 20140819050 (holotype: BAU!)

Plants medium-sized, 0.9–1.6 cm high, growing in dense turfs, green to reddish brown in upper part, reddish-brown to brownish in lower part. Stems irregularly branched, hyalodermis weakly differentiated, sclerodermis present, central strand developed; axillary hairs filiform, short, usually 3–4 cells long, with one brown basal cell and hyaline upper ones. Rhizoidal tubers absent. Leaves appressed when dry, patent to spreading when moist, ovate-lanceolate to oblong-lanceolate, 1.45–1.95 × 0.45–0.75 mm, channeled ventrally in the upper part, weakly sheathing; lamina completely or irregularly bistratose in upper middle part of leaf, brownish with KOH; apex obtuse; margins entire, recurved from leaf base to just below apex, not decurrent at base, 2–3-stratose; costa percurrent, 70–87.5 μm wide at base, ventral cells of the costa in the upper half oblate or quadrate, smooth; dorsal surface cells of the costa in the upper half oblate or quadrate, smooth; costa cross-section elliptical, with (2)3 layers of guide cells, with 4–8 cells in each layer, without ventral stereids, 2–4 layers of dorsal stereids, lunulate in shape, generally without hydroids, ventral surface cells differentiated, weakly bulging, smooth, dorsal surface cells differentiated, smooth; upper and middle laminal cells irregularly subquadrate to oblate, 5–6.5 × 4.5–7.5 μm, thin-walled, smooth, not bulging; basal juxtacostal cells short-rectangular to rectangular, 15–32.5 × 7.75–11.25 μm, thin walls, smooth; basal marginal cells quadrate to oblate, 5–8.75 × 10.25–14.5 μm, with thickened transverse walls and thin longitudinal walls, smooth. Gemmae absent. Dioicous. Sporophytes not seen.

Paratypes:— CHINA. Tibet: Ngamring County, on soil, 29°23′10′′N, 86°52′29′′E, 4532 m, 15 Auguest 2014, Xiao-Ming Shao & Jin Kou 20140815037 (BAU).

Etymology:— The specific epithe, obtusus , refers to the obtuse leaf apex, a noteworthy character that differentiates its most similar species, D. rigidulus var. subulatus .

Distribution and ecology

The new species grows on rocks and soil and is known only from two localities in Nagarzê County and Ngamring County. Nagarzê County is located in northern foot of middle part of the Himalayas, and is also the highest area in the Shannan Prefecture with an average elevation of 4500 m. This area belongs to plateau temperate Semi-arid monsoon climate, with adequate lighting, an annual rainfall of about 376 mm. Ngamring County has an average elevation of above 4000 m and belongs to warm-moist semi-arid climate. Owing to harsh environment, the two localities are covered mainly in herbs, lichens and bryophytes ( Li et al. 2004, Liu et al. 2015).

Figures

FIGURE 1. Didymodon obtusus. A. Plant when dry (scale in mm). B. Plant when moist (scale in mm). C. Cross-section of stem. D. Leaves. E. Upper part of costa (dorsal). F. Upper part of costa (ventral). G. Mid-leaf cells. H. Basal juxtacostal cells. I. Basal marginal cells. J. Axillary hairs. Scale bar (as shown on C): C, J = 100 μm; D = 1 mm; E–I = 40 μm. All from holotype.

FIGURE 2. Didymodon obtusus. A. Leaf apex (dorsal). B. Leaf apex (ventral). C–H. Transverse section of leaf, sequentially from apex to base. Scale bar (as shown on H): A–H = 100 μm. All from holotype.