Fissidens crassinervis Thwait. & Mitt., J. Linn. Soc. Bot. 13: 323. 1873, hom. illeg., non Fissidens crassinervis Sande-Lac., Verh. Kon. Ned. Akad. Wetensch., Afd. Natuurk. 13: 3. Pl. 2: a.1872. Fissidens laxus Sull. & Lesq., Proc. Amer. Acad. Arts Sci. 4: 275. 1859. Type. China: Hong Kong, C. Wright s.n. (holotype FH). Fissidens mittenii Par., Ind. Bryol. 477. 1894.

Plants small, growing in loose tufts, usually brownish or reddish brown. Leafy stems simple, 2.4–5.2 mm long, 1.0–2.1 mm wide; axillary hyaline nodules lacking; central strand weakly differentiated. Leaves in 4–12 pairs, lower leaves very small, loosely arranged; upper leaves much larger than the lower leaves, densely arranged, lanceolate, 0.7–1.4 mm × 0.2–0.3 mm, acute to narrowly acute at apex; base of dorsal laminae wedge-shaped to rounded; vaginant laminae 1/2 the leaf length, unequal; costa stout, percurrent to shortly excurrent; margins crenulate to indistinctly serrulate; cells of apical and dorsal laminae quadrate to irregularly hexagonal, 10–24 µm long, thick-walled, transparent, smooth; cells of upper half of vaginant laminae similar to those of apical and dorsal laminae, but narrower toward the base. Polyoicous. Perichaetial leaves differentiated, upper end of vaginant laminae rounded, open to costa, cells at upper end of vaginant laminae elongate, irregularly rhombic, thick-walled. Archegonia 245–390 µm long. Setae 2.5–2.9 mm long, smooth; capsules erect, symmetrical; urns ovoid, 0.4–0.5 mm long; exothecial cells quadrate to broadly oblong, thin-walled with distinctly thickened corners, distinctly mammillose; opercula conic-rostrate, ca. 0.4 mm long; peristome teeth 0.28 mm long, 36 µm wide at base, spirally thickened above, densely covered by minute papillae below.

Type. Suriname: Weigelt s.n.

Chinese specimens examined: FUJIAN: Nan-qing Co., G.-C. Zhang & J.-Y. Feng 321, 381 (IFSBH, SYS), M. Zang 408 (HKAS, NICH). GUANGDONG: Ding-hu Shan (Mt.), Redfearn et al. 34413 (MO); Gao-yao Co., H. Wu B90 (IBSC, SYS); Guang-zhou City, P.-J. Lin 1693, 3412 (IBSC, SYS). HAINAN: Ba-wang-ling (Mt.), Z.-H. Li 3197 (IBSC, SYS); Jian-feng-ling (Mt.), Z.-H. Li 85–196 (SYS); Le-dong Co., Redfearn 35945 (MO); Wu-zhi Shan (Mt.), Z.-H. Li 2047, 2352 (SYS). TAIWAN: Ilan Co., S.-H. Lin 8777 (NICH, TUNG); Nan-tou Co., Koponen 17425, 18476 (H); Ping-tung Co., Shevock 15053 (MO). YUNNAN: Jing-hong Co., Magill et al. 7800 (MO); Meng-hai Co., Magill 7959 (MO). ZHEJIANG: Yan-tang Shan (Mt.), D.-K. Li & C.-H. Gao 8537 (SHM, SYS).

Habitat: on soil; Distribution: China, Japan, Nepal, India, Sri Lanka, Myanmar, Thailand, Vietnam, Malaysia, Singapore, Indonesia, the Philippines, and South America.

The leaf shape of Fissidens pellucidus is variable. In the holotype the leaves are narrow with excurrent costa and the bases of dorsal laminae are wedge-shaped. However, in most Chinese specimens the leaves are broader mostly with percurrent costa (rarely excurrent) and the bases of the dorsal laminae always rounded. This species is closely allied to F. guangdongensis. The distinction between the two species is discussed under the latter.

Illustrations: Z.-H. Li 1985 (Fig. 15, a–m, as Fissidens laxus).