4. Oligotrichum Cand. in Lam. & Cand. 小赤藓属 xiao chi xian shu
Fl. Franc. (ed. 3) 2: 491. 1805. Polytrichum sect. Oligotrichum (Cand.) Arnott, Mém. Soc. Linn. Paris 5: 322. 1827. Polytrichum subgen. Oligotrichum (Cand.) Mont. in Orbigny, Dict. Univ. Hist. Nat. 8: 400. 1849.
Plants slender or rarely robust, small to large, yellowish green, brownish green or reddish brown, erect, usually in tufts, rarely gregarious. Stems often with stoloniferous and innovated branches, numerous rhizoids at base; central strand inconspicuously developed. Leaves oblong-lingulate to oblong-lanceolate, slightly concave, strongly crisped when dry, erect spreading when moist, closely appressed on stems, not clearly sheathing at base; margins distinctly serrate or entire; costa rather broad, ending in the acumen or excurrent into subula; lamellae wavy or undulate, densely spaced on the ventral surface of costa, with several low lamellae or spines on the back; leaf cells unistratose; median cells rounded oval, quadrate, or irregularly subquadrate; basal cells rectangular or irregular, slightly thick-walled. Dioicous. Perigonia in rosettes, perigonial bracts sometimes with lamellae at its apex. Innovations often growing from the middle of perigonia. Setae yellowish or reddish brown, straight; capsules cylindrical or oblong-ovoid, erect or patent, usually single; exothecial cells smooth, stomata few, with inner and outer air chamber; columella with 4 longitudinal wings; peristome teeth 32, unequal in length; opercula conic, long or short beaked. Calyptrae cucullate, covered with sparse or dense cilia. Spores spherical, verrucose.