Fissidentaceae Schimp., Coroll. Bryol. Eur. 1855.
Li Zhi-hua and Zen Iwatsuki
Plants minute to fairly large, green to dark green or reddish brown, gregarious or tufted, terrestrial, saxicolous, lignicolous or aquatic. Stems mostly erect, simple or irregularly branched; rhizoids basal or axillary, smooth or papillose; axillary hyaline nodules developed or lacking; central strand present or absent. Leaves distichous (in two rows), alternate and complanate, consisting of three parts: 1) the vaginant laminae—a sheathing basal part that clasps the stems; 2) the apical laminae—the part above the vaginant laminae on the same side of the costa; 3) dorsal laminae—the whole part on the opposite side of the costa; costa usually well developed, percurrent, excurrent, or ending below the leaf apex, rarely indistinct or lacking; limbidia usually developed in varying degrees or lacking, if present, composed of narrow, thick-walled and elongated cells, usually one cell thick, rarely multi-stratose; leaf cells variable, smooth, mammillose or pluripapillose, mostly 1 layer, sometimes 2- to multi-stratose, irregularly hexagonal to rounded, isodiametric or elongate. Dioicous or monoicous. Perichaetia terminal or in axils of leaves; perichaetial and perigonal leaves usually differentiated. Setae mostly elongate, sometimes very short to immersed; capsules erect, symmetrical, or inclined, curved and asymmetrical; annuli absent; opercula conic, short to long rostrate; peristome single,16 teeth, red to reddish brown, upper portion usually divided into two spirally thickened or articulate filaments, occasionally peristome teeth absent. Calyptrae cucullate or mitrate, usually smooth. Spores small, spherical, smooth to finely papillose.
Although the Fissidentaceae may consist of more than one genus, the family is widely considered to include a single genus, Fissidens Hedw., with six subgenera. In this floristic treatment, the subgenera or sections are not recognized, following that of Z.-H. Li (1996).