Trichostomum planifolium Zander 1993

Trichostomum planifolium was synonymized with T. crispulum by A. Stoneburner (1985) and Stoneburner and R. Wyatt (1985), but is retained here because it is monoicous. The leaf margins are sometimes inflexed distally, as in Weissia, and it was synonymized with Weissia perligulata by L. R. Stark (1996), the type of which has weakly inflexed or laxly involute distal leaf margins. The costa of T. planifolium and the similar T. brachydontium is quite thick and protrudes strongly abaxially. The gametophyte of Trichostomum planifolium is essentially that of T. brachydontium. It differs from Weissia inoperculata in having a slightly shorter apiculus, in addition to the stegocarpic capsule. Some plants of the type of W. perligulata (= T. planifolium) have comparatively very wide leaves with costa ending below the broadly rounded apex, yet other plants have leaves with costae that are percurrent or shortly excurrent from an obtuse or rounded acute apex, and in all leaves the papillae are large and short-spiculose, though not as salient as those of specimens assigned to W. andersoniana (= W. ligulifolia); S. Flowers (1973) suspected that W. ligulifolia and W. perligulata are synonymous, but found sexual differences between them on the basis of a few specimens; here the former is distinguished by the strongly involute distal laminal margins and distal lamina ca. 12-18 cells across on one side of the costa just above mid leaf versus margins plane or weakly incurved to laxly inflexed, and lateral lamina 25-30 cells across for T. planifolium.

Stem rounded-pentagonal in section. Leaves flattened, ovate to elliptical, distal margins plane or weakly erect or rarely broadly involute, entire, not bordered; apex rounded or rounded-acute, plane to weakly concave, keeled or cucullate; basal cells evenly differentiated across leaf base or as a U, only weakly running up margins if at all, not distinctly enlarged submarginally; distal laminal cells pluripapillose with low papillae; mucro short-conic, of 3-4 cells. Sexual condition autoicous. Peristome teeth absent to short-lanceolate.

Plants small, to 12 mm high, dark green or reddish brown, in dense tufts. Stems erect, usually irregularly branched, densely foliate. Leaves crisped when dry, erecto-patent when moist, narrowly ovate-lanceolate or narrowly ligulate, broadly acute or obtusely pointed, upper lamina often keeled; margins entire, usually plane; costa stout, percurrent or excurrent as a mucro; upper leaf cells rounded-hexagonal, moderately thick-walled, green and obscure, each cell with several large, circular papillae on both surfaces; basal cells slightly elongate, irregularly short-rectangular, smooth, hyaline. Autoicous. Setae 5–7 mm long, yellowish; capsules erect, oblong-ellipsoidal; peristome teeth erect, linear, short, undivided, papillose.

Distribution: China, Japan, and Russia.

Habitat: on rocks, forest ground, or tree trunks; also on rocks and soil at roadsides or near streams.

Weissia planifolia Dixon, Rev. Bryol. 55: 179, fig. 1. 1928; Trichostomum perligulatum (H. A. Crum) R. H. Zander; W. perligulata H. A. Crum; W. sweetii E. B. Bartram

Weissia cucullifolia Dix. & Sak. in Sak., Bot. Mag. (Tokyo) 53: 63, f. 7. 1939. Weissia platyphylla Broth., Hedwigia 38: 205. 1899, hom. illeg.

Trichostomum planifolium là một loài Rêu trong họ Pottiaceae. Loài này được (Dixon) R.H. Zander miêu tả khoa học đầu tiên năm 1993.