Ptychodium leucodonticaule C. Müll., Nuovo Giom., Bot. Ital. n. ser. 4:268.1897. Type. CHINA. Schen-si: In cacumine montis Sun-san, inter lichens, Nov 1895, J. Giraldi 1494 = (FI!, herb. Levier).
Homalothecium sinense Par. & Broth., Rev. Bryol. 35: 128. 1908, syn. nov. Type. CHINA. Kiang Sou (Kiangsu): Zi Ka Wei, prope Shang-Hai, Feb 1908, R. P. Courtois (H-BR!, syntype).
Homalothecium perimbricatum Broth., Sitzungsber. Akad. Wiss. Wien Math. Nat. Kl. Abt. 1,131: 220. 1922, syn. nov. Type. CHINA. Hunan: In ditione oppidi Tsingtschou ad rupes proce vie. Sandjingtjiau, substr. arenaceo, ca. 400 m, 30 Jul 1917, Handel-Mazzetti 11017 (H-BR!, holotype).
The types of H. leucodonticaule, H. perimbricatum and H. sinense were compared and other specimens of H. perimbricatum from China in H-BR studied (Handel-Mazzetti 212, 309). They proved to be identical in having a large area of fairly thin-walled short-rectangular to quadrate basal leaf cells. In addition, the type specimens of H. sinense and H. perimbricatum have rather shortly acuminate leaf apices, which have short marginal teeth to almost toothless margins. Leaf bases are broadly rounded. The type specimen of H. leucodonticaule also has thin-walled basal leaf cells which are somewhat smaller than those of H. perimbricatum and H. sinense. The leaf apex as well is more long-acuminate and has sharper apical teeth. According to the description and illustrations provided by Takaki (1955) of the Japanese specimens of H. perimbricatum and H. laevisetum Sande Lac, these characters seem to be rather variable. Thin-walled basal leaf cells separate H. leucodonticaule from H. laevisetum (=H. tokiadense (Mitt.) Besch.) which has distinctly thick-walled basal leaf cells (Fig. 2a-h). This was confirmed by studying the types of H. laevisetum and H. tokiadense (in h-br). The leaves of H. laevisetum are also long-acuminate and the apical leaf margin distinctly toothed. According to Takaki (1955), fairly shortly acuminate variations exist.