5. Rhizomnium nudum (Britt. & Williams) T. Kop. 圆叶毛灯藓 yuan ye mao deng xian
Ann. Bot. Fenn. 5: 143. 1968. Mnium nudum Britt. & Williams, Bryologist 3: 6. 1900. Type: U.S.A. Idaho, Leiberg s.n.
Plants medium-sized, dark brown to reddish brown, in dense tufts. Stems erect, ca. 3.0 cm high, sparsely foliate, with dense rhizoids at base. Leaves twisted when dry, spreading when moist, lower leaves smaller, nearly rounded, ca. 2.0 mm wide, upper leaves larger, broadly obovate or elliptical, ca. 6.0 mm × 4.5 mm, narrowed and not decurrent at base, rounded-obtuse at apex; margins entire, bordered by 2–3 rows of irregularly elongate cells, marginal cells weakly to distinctly porose; costae ending above mid-leaf; leaf cells regularly hexagonal or pentagonal, 65–110 µm × 40–60 µm, thin-walled, not clearly porose. Dioicous. Inner perichaetial leaves small, elongate-elliptical. Setae solitary, ca. 2.5 cm long, brownish; capsules ovoid-cylindrical, horizontal.