Fissidens dubius Palisot de Beauvois 1805

In contrast to Fissidens adianthoides, F. dubius has smaller, irregularly 2-stratose, obscure laminal cells. Subterranean, irregularly globose, multicellular rhizoidal gemmae have been reported for F. dubius as well as F. osmundioides and F. taxifolius in Europe and Japan. Z. Iwatsuki and T. Suzuki (1982) cited the occurrence of dwarf male plants (small perigonial stems located on the leaves of perichaetial plants) in Japanese specimens.

Plants to 25 × 3.5 mm. Stem usually branched; axillary hyaline nodules absent; central strand present. Leaves as many as 25 pairs, often undulate, oblong to lanceolate, obtuse to acute, often apiculate, to 3.5 × 0.7 mm; dorsal lamina truncate-rounded proximally, ending at insertion, not decurrent; vaginant laminae ²/3 the leaf length, ± unequal, minor lamina ending near margin; margin crenulate to crenulate-serrulate but unevenly serrate at leaf apex, elimbate; costa ending a few cells before apex to percurrent, taxifolius-type; laminal cells irregularly 2-stratose in dorsal and ventral laminae, ± obscure, smooth, bulging, firm-walled, rounded-hexagonal, 7-10 µm, 3-4 rows of marginal cells thinner, walls slightly thicker, forming a pale marginal band. Sexual condition dioicous; perigonia on short axillary branches and elongate stems; perichaetia on short axillary branches, mostly near proximal ends of stems. Sporophytes 1 per perchaetium. Seta to 11 mm. Capsule theca slightly inclined, slightly arcuate, bilaterally symmetric, to 1.8 mm; peristome taxifolius-type; operculum 1-1.4 mm. Calyptra cucullate, smooth, 1.8 mm. Spores 13-20 µm.

Plants green to brownish. Leafy stems simple, rarely branched, 10–50 mm long, 3.5–5.0 mm wide; axillary hyaline nodules not differentiated; central strand well differentiated. Leaves in 13–58 pairs, rather densely arranged; the lowermost leaves small, upper leaves much larger; middle to upper leaves lanceolate, 3.2–3.5 mm × 0.7–0.8 mm, distinctly crisped when dry, acute to narrowly acute at apex; base of dorsal laminae rounded to shortly decurrent; vaginant laminae 3/5 – 2/3 the leaf length, equal or slightly unequal; costa stout, percurrent; margins irregularly toothed near the apex, finely crenulate to serrulate below, bordered by a lighter colored band of 3–5 rows of incrassate, smooth, paler cells, this lighter-colored band one cell to rarely two cells thick in cross section, much clearer on apical and dorsal laminae than on vaginant laminae; cells of apical and dorsal laminae usually rounded-hexagonal, rarely elliptical-ovate, 10–11 µm long, distinctly mammillose, obscure, apical laminae one cell thick, but occasionally two 2 cells thick; cells of vaginant laminae similar to those of apical and dorsal laminae, but less mammillose. Phyllodioicous. Male plants small, ca. 1 mm long, growing from vaginant laminae of female plants. Female inflorescences axillary. Perichaetial leaves much smaller than stem leaves, ovate-lanceolate, 1.0–1.3 mm long. Archegonia ca. 300 µm long. Setae lateral, 5–8 mm long, smooth; capsules slightly inclined, asymmetrical; urns 0.8–1.4 mm long; exothecial cells quadrate to oblong with thickened vertical walls and thinner transverse walls; opercula long rostrate, ca. 1.6 mm long; peristome teeth 0.5–0.6 mm long. Calyptrae campanulate, ca. 1.6 mm long.

Distribution: China, Korea, Japan, Nepal, India, Sri Lanka, Indonesia, the Philippines, New Guinea, Africa, Europe, and Central and North America.

Habitat: mostly on rocks, rarely on tree trunks or on soil.

Fissidens adianthoides var. semicristatus Grout; F. cristatus Mitten; F. cristatus var. winonensis (Renauld & Cardot) Grout; F. decipiens var. winonensis Renauld & Cardot; F. floridanus Lesquereux & James

Fissidens cristatus Wils. ex Mitt., J. Proc. Linn. Soc., Bot., Suppl. 1: 137. 1859. Fissidens decipiens De Not., Atti R. Univ. Genova 1: 479. 1869. Fissidens micro-japonicus Par., Rev. Bryol. 35: 125. 1908. Type. China: Jiangsu (Kiang Sou), Li-Ku-Kei, II. 1908. R. P. Courtois 1076 (isotype ? H-BR). Fissidens obsoleto-marginatus C. Müll., Nuovo Giorn. Bot. Ital., n. ser. 3: 89. 1896. Type. Shaanxi (Schen-si), in medio monte Kuan-tou-san and Zu-lu, VIII 1894, P. J. Giraldi s.n.