Fissidens involutus Wils. in Hooker’s J. Bot. Kew Gard. Misc. 9: 294. 1857, nom. nud. Fissidens irrigatus Broth., Sitzungsber. Kaiserl. Akad. Wiss. Math.-Naturwiss. Cl. 133: 559. 1924. Type. China: Sichuan (Setschwan), Handel-Mazzetti 1895 (holotype H-BR). Fissidens plagiochiloides Besch., J. Bot. (Morat). 12: 293. 1898. Type. China: Yunnan, Tsang chen, Delavay 1872 (holotype PC; isotypes FI, H-BR). Fissidens subinteger Broth., Symb. Sin. 4: 10. 1929. Type. China: Hunan, Handel-Mazzetti 12216 (holotype H-BR).

Plants medium-sized to large, yellowish to brownish. Leafy stems rigid, simple or branched, 10–50 mm long, 2.0–5.0 mm wide; axillary hyaline nodules not or only weakly differentiated; central strand slightly differentiated. Leaves in 16–25 pairs, with inrolled apices even when moist; lower leaves often decayed; middle to upper leaves lanceolate, 1.3–4.0 mm × 0.3–1.0 mm, acute at apex; base of dorsal laminae rounded; vaginant laminae more or less unequal, 1/2 –3/5 the leaf length; costa stout, brownish red, percurrent, a row of cells on both sides of the costa rectangular, smooth and pellucid; margins finely serrulate or crenulate; cells at apex smooth, thick-walled, forming a paler region; cells of apical and dorsal laminae quadrate to rounded-hexagonal, 3.5–7.0 µm long, thin-walled, markedly mammillose and obscure; cells of vaginant laminae similar to those of apical and dorsal laminae, but much larger, smooth, with thicker walls toward the base near costa. Dioicous. Archegonia terminal on main stems, 568–610 µm long. Perichaetial leaves indistinctly differentiated, slightly narrower and shorter than stem leaves. Sporophytes not seen.

Syntypes. Sikkim: J. D. Hooker 641 (lectotype NY).

Chinese specimens examined: FUJIAN: Wuyi Shan (Mt.), D.-K. Li & C.-H. Gao 13448 (SHM, SYS). GUANGXI: Long-sheng Co., P.-C. Wu & Y.-X. Lin 975b (PE, SYS). GUIZHOU: Fan-jing Shan (Mt.), C. Gao & J.-Y. Feng 31718 (IFSBH, SYS); Sui-yang Co., C. Gao & J.-Y. Feng 32940 (IFSBH, SYS). HUBEI: Shen-nong-jia (Mt.), P.-C. Wu 470 (MO). JIANGXI: Lu Shan (Mt.), R.-L Hu 2398 (HSNU, SYS). SHAANXI: Tai-bai Shan (Mt.), Z.-P. Wei 4916 (IBSC, SYS). SICHUAN: Liang Shan (Mt.), G.-C. Zhang & T. Cao 21417 (IFSBH, SYS); Omei Shan (Mt.), D.-K. Li 15315 (SHM, SYS); Mian-yang Co., Redfearn 35597 (MO); Tian-quan Co., C. Gao et al. 17594 (IFSBH, SYS); Ya-an Co., C. Gao 17381 (IFSBH, SYS); Yan-bian Co., M.-Z. Wang 20210 (PE, SYS). TAIWAN: Kao-hsiung Co., S.-H. Lin 2056a (NICH, TUNG); Nan-tou Co., S.-H. Lin 4175a (NICH, TUNG); Tai-tung Co., S.-H. Lin 13209 (NICH, TUNG). XIZANG: Mo-tuo Co., Y.-G. Su 3796(2) (HKAS, NICH). YUNNAN: W.-X. Xu 11428 (H, IBSC, SYS); Chu-xiong Co., Redfearn & S. He 1759 (MO); Gong-shan Co., M.-Z. Wang 9714 (PE, SYS); Meng-hai Co., Magill et al. 7965 (MO); Wei-xi Co., M.-Z. Wang 5157a (PE, SYS); Yang-bi Co., Redfearn 367 (MO). ZHEJIANG: Lin-an Co., P.-C. Wu 8081 (MO); Tian-mu Shan (Mt.), D.-K. Li 3596 (SHM, SYS).

Habitat: mostly on moist rocks, rarely on sandy soil; Distribution: China, Japan, Nepal, India, Myanmar, Thailand, Vietnam, and the Philippines.

This species is characterized by its leaves with a paler region composed of smooth and thick-walled cells at the apex and the differentiation of a row of rectangular, smooth, hyaline cells along both sides of the costa.

Illustrations: Pl. 81, figs. 7–12.