Fissidens angustifolius is subsumed under F. biformis and F. coorgensis under F. zollingeri. It appeared that F. biformis sensu Gangulee et Eddy is F. zollingeri.
Fissidens angustifolius Sull. and F. zollingeri Mont, are well-known pantropical limbate species characterized by limbidia reaching the leaf apex and the insertion of the dorsal lamina, small, but distinct axillary nodules, large, inflated juxta-costal vaginant laminai cells, stems that are often frondiform, but can have pinnately arranged leaves and subgenus Aloma sporophytes i.e. with 32 columns of exothecial cells and a scariosus type of peristome. They differ in the laminal cells, those of F. angustifolius are mammillose, those of F. zollingeri smooth.
References to F. biformis Mitt, are confusing. The species was described by Mitten and reduced to F. zollingeri Mont, by Fleischer (1901), but was retained as species next to F. zollingeri by Gangulee (1971) and Eddy (1988). Gangulee l.c. listed F. coorgensis Broth, as synonym of F. biformis. Iwatsuki and Suzuki (1982) did not include F. biformis, but in a note with F. zollingeri state that its type specimen has unipapillose cells. This note went probably unobserved by Eddy (1988) who described F. biformis as smooth-celled and listed F. coorgensis Broth, as synonym. The purpose of the present research was to establish whether F. zollingeri, F. biformis and F. coorgensis are conspecific. Iwatsuki & Suzuki's observation that the laminal cells of the type of F. biformis are unipapillose (strictly speaking they are highly mammillose) was confirmed. Consequently this species is conspecific with F. angustifolius rather than with F. zollingeri which has smooth, plane laminal cells. The name F. biformis has priority. Examination of the type of F. coorgensis showed that it has smooth cells and is F. zollingeri.
According to the descriptions by Gangulee l.c. and Eddy l.c. F. biformis has smooth laminal cells. This suggests that F. biformis sensu these authors is F. zollingeri. This is supported by the fact that all synonyms cited by these authors, viz. F. coorgensis and F. xiphioides M. Fleisch, are F. zollingeri, too.
Fissidens biformis Mitt., J. Proc. Linn. Soc., Bot. 2; 141. 1859 - Type: SRI LANKA [Ceylon], ad Matale, Gardner 626 (label; Ceylon, ad Matale, Gardner 55 (626) (lectotype (Iwatsuki in sched.): NY 00 966583!; isotype; NY 00966584!).
F. angustifolius Sull, Proc. Amer. Acad. Arts 5: 275. 1861 - Type: CUBA, wet places on the ground in dense woods; distributed as Sullivant, Musci Cubensis 18 (holotype: FH (not seen), isotypes BM (not recently seen), NY (not recently seen). According to Pursell (2007) several packets contain only F. zollingeri Mont.; this appeared to be true for the L-specimen). — syn. nov.
Fissidens zollingeri Mont., Ann. Sci. Nat. Bot. 4; 114, 1845 - Type: INDONESIA, in terra turfosa insulae Javae, Zollinger 1604 (holotype: PC-Mont; isotype; PC-Besch.). Fissidens xiphioides M. Fleisch., Hedwigia 38 (Beibl.); 125. 1899 — Type: INDONESIA, Java, auf lehmigem, festem Boden im Culturgarten bei Buitenzorg, M. Fleischer (lectotype (Iwatsuki & Suzuki,1982): FH; isotypes distributed as Fleischer, Musci-Archipelagi Indici ser I. 14 (1898); H-BR!) - synonymized by Iwatsuki & Suzuki (1982). Fissidens coorgensis Broth., Rec. Bot. Surv. India 1 (12): 316. 1899 - Type: INDIA, Coorg, dry shady clay banks near Sidapur, II 1898, Walker 267 (holotype: H-BR (H 1606047)!) - considered a synonym of F. biformis by Gangulee (1971). — syn. nov.