12. Gymnostomum Nees & Hornsch. 净口藓属 jing-kou xian shau
Bryol. Germ. 1: 153. 1823, nom. cons.
Plants perennial, small to rather large, in dense tufts, growth by annual renovation at the stem apices. Stems erect, simple, rarely branched; central strand present, weak. Leaves contorted when dry, erect-spreading when moist, oblong-elliptically lanceolate to narrowly lanceolate; margins plane, entire; costa stout, usually ending below the apex; upper leaf cells small, rounded quadrate to rounded hexagonal, densely papillose; basal cells irregularly rectangular, smooth, hyaline or pale yellowish. Dioicous. Perichaetial leaves somewhat sheathing at the base. Setae straight, slender; capsules erect, oblong-ovoid; peristome teeth absent; opercula conic-rostrate, with a long beak, deciduous or persistent with columella. Calyptrae cucullate. Spores yellowish brown, smooth or densely papillose.