2. Hydrogonium arcuatum (Griff.) Wijk & Marg., Taxon. 7:289. 1958; Barbula arcuata Griff., Calcutta J. Nat. Hist. 2: 491. 1842.
Hydrogonium comosum (Dozy & Molk.) Hilp., Beih. Bot. Centralbl. 50(2): 622. 1933. Barbula comosa Dozy & Molk., Ann. Sci. Nat., Bot., sér. 3, 2: 299. 1844.
Plants stiff, in dense tufts. Stems erect, simple, rarely branched, radiculose at the base. Leaves erectopatent, ovate- or triangular-lanceolate, gradually acuminate at the apex; margins entire, plane or weakly revolute; costa stout, ending just below the apex; upper leaf cells quadrate to pentagonal, orderly arranged, thin-walled, smooth; basal cells irregularly rectangular, thin-walled, smooth, hyaline. Sporophytes not seen.
Type. India: Assam.
Chinese specimens examined: ANHUI: Huang Shan (Mt.), M. Zang 6110 (HKAS). GUIZHOU: Du-yun Co., Handel-Mazzetti 10756 (H). HEBEI: Dong-ling (Mt.), L.-Q. Yu 449 (PE). HENAN: Lan-chuan Co., H.-J. Yu 3057 (MO, PE); Xi-chuan Co., C.-Z. He 6046 (MO, PE). HUNAN: Da-yong Co., D.-K. Li 18143 (HKAS, SHM); Sang-zhi Co., D.-K. Li 19294 (HKAS, SHM). JIANGSU: Li-yang Co., D.-K. Li 18924 (HKAS, SHM). JILIN: Wang-qing Co., C. Gao 8587 (HKAS, IFSBH). LIAONING: Kuan-ding Co., C. Gao 001411 (HKAS, IFSBH). SHAANXI: Hu Co., M. Wang 641 (HKAS). SICHUAN: Le-shan Co., P.-C. Chen 5–737 (PE); Wen-chuan Co., J.-X. Luo 3675 (PE). TAIWAN: Suzuki 2651, 1673 (H). XIZANG: Jiang-zi Co., M. Zang 828 (HKAS); Mo-tuo Co., Y.-G. Su 2388 (HKAS); Ya-dong Co., M. Zang 39-a (HKAS). YUNNAN: Kun-ming City, Z.-M. Li 365-c (HYUB); Li-jiang Co., Croat 77543 (MO); Meng-la Co., L. Zhang 26275 (HKAS). ZHEJIANG: Hang-zhou City, R.-L. Hu 2 (HKAS); western Tian-mu Shan (Mt.), M. Zang 241 (HKAS).
Habitat: on rocks, soil walls of river banks or on bases of tree trunks; Distribution: China, Japan, Nepal, India, Indonesia, and the Philippines.
Illustrations: Pl. 123, figs. 5–9.
