西藏大帽藓

Plants rather small, 5–7 mm high, green above, brown below. Stems simple; central strand not well developed. Leaves slightly twisted when dry, erect-spreading when moist, 1.7–2.3 mm, lingulate, gradually narrowed to an obtuse apex; margins plane; costa single, stout, ending below or at the apex; upper cells irregularly rounded to quadrate, 13–15 µm wide, densely papillose; basal cells oblong, 26–39 µm x 15–18 µm, with reddish brown and slightly thickened transverse walls; 3–4 rows of marginal cells linear, 30–50 µm x 3–5 µm, thin-walled. Autoicous. Perichaetial leaves similar to upper stem leaves. Setae erect, 3.5–7.0 mm long; capsules oblong-ovate, erect, about 1 mm long, mouth contracted, with distinct reddish longitudinal ribs; peristome single teeth, lanceolate, hyaline above, yellowish and perforate below, densely papillose throughout; opercula with a long, straight beak. Calyptrae short-cylindric, covering the whole capsule, golden to golden brown, basal margin smooth or nearly so, with short rostrum, 0.3–0.4 length of calyptra. Spores 31–34 µm in diameter, with regular, large, warty papillae.

Type. China: Xizang (Tibet), T. Thomson 250 (holotype NY).

Chinese specimens examined: XINJIANG: Mts. Arjin, Achuff 7249a (ALTA, Herb. D. Horton), 7250 (Herb. D. G. Horton), 7267 (ALTA, Herb. D. G. Horton, IFSBH).

Habitat: high elevations ca. 5000 m, on calcareous soil in Kobresia turf and in Leontopodium nanum cushions on exposed ridges; Distribution: endemic to China.

Encalypta tibetana appears to be most closely related to E. rhaptocarpa s. str. The well-developed peristome, ribbed capsules and basal leaf cells with thickened, reddish walls, and a narrow, marginal border of yellowish cells are typical features of the latter taxon. Encalypta tibetana differs from E. rhaptocarpa in having its leaves muticous, costa ending at the apex or below the apex, and in having short capsules and calyptrae. However, these features have been observed in arctic and other alpine populations that have been regarded as E. rhaptocarpa s. lat. Future study on the E. rhaptocarpa-E. vulgaris complex may prove that E. tibetana and E. rhaptocarpa are synonymous.

Illustrations: Pl. 105, figs. 1–11.