Monographs Details: Ctenidium
Authority: Buck, William R. 1998. Pleurocarpous mosses of the West Indies. Mem. New York Bot. Gard. 82: 1-400.
Description:Genus Description - Plants small to medium-sized, in often lustrous, soft, green to yellow-green to yellow-brown, often extensive, dense mats. Stems creeping to ascending, irregularly to regularly pinnately branched, the branches sometimes branched, unequal, not complanate-foliate; in cross-section without a hyalodermis, with small thick-walled cells surrounding larger thinner-walled cells, central strand present; pseudoparaphyllia foliose, large; axillary hairs with 1-4 short hyaline basal cells and 1 to several mostly elongate hyaline distal cells. Stem and branch leaves differentiated, stem leaves erect-spreading to squarrose-recurved, often secund, broadly ovate, abruptly acuminate, often plicate, especially when dry, cordate and broadly decurrent at base; margins serrate to serrulate throughout, plane to erect; costa short and double or none; cells linear to oblong-linear, low-prorulose at upper and sometimes lower ends at back, sometimes smooth, firm-walled, becoming shorter in a few rows across the insertion; alar cells decurrent, subquadrate to oblong, enlarged. Branch leaves smaller than stem leaves, erect-spreading to squarrose, obscurely homomallous to falcate-secund, lanceolate to ovate-lanceolate, gradually acuminate, concave, subplicate, short-decurrent; margins serrate to serrulate above, subentire to serrulate below, plane to recurved; costa short and double or none; cells linear to oblong-linear, conspicuously prorulose at upper and sometimes lower ends at back, firm-walled, becoming shorter in a few rows across the insertion; alar cells subquadrate to short-rectangular. Asexual propagula none. Dioicous or phyllodioicous. Perichaetial leaves erect with spreading apices, oblong to broadly oblong, abruptly long-acuminate, concave; margins serrulate above, serrulate to entire below, plane; costa short and double or none; cells oblong-linear to linear-flexuose, usually smooth, becoming laxly rectangular toward the insertion; alar cells not differentiated. Setae elongate, smooth or rarely roughened, reddish; capsules inclined to horizontal, arcuate, asymmetric, ovoid to broadly cylindric; exothecial cells ± isodiametric, thick-walled on vertical walls, thinner-walled on crosswalls; annulus differentiated; operculum conic, mostly short-rostrate; peristome double, exostome teeth shouldered, bordered, on the front surface cross-striolate below, sometimes with overlying papillae, papillose above, trabeculate at back; endostome with a high basal membrane, segments keeled, perforate, ca. as long as the teeth, cilia in groups of 23, well developed to rudimentary. Spores spherical, finely papillose. Calyptrae cucullate, usually hairy, smooth.
Discussion:Ctenidium (Schimp.) Mitt., J. Linn. Soc., Bot. 12: 509. 1869; Hypnum subgen. Ctenidium Schimp., Syn. Musc. Eur. 631. 1860; Stereodon sect. Ctenidium (Schimp.) Mitt., J. Linn. Soc., Bot. 8: 153. 1864.
Discussion. Ctenidium has differentiated stem and branch leaves and in many ways is like Mittenothamnium but is distinguished by decurrent leaves, especially those of the stem, with a better alar development. Ctenidium is also characterized by serrate leaves with prorulose cells, and stem leaves that are broadly ovate and abruptly tapered to an acuminate apex. A relationship to Mittenothamnium is unmistakable not only because of gametophytic characters but also because of the unequally thickened exothecial cells.
Only a single species is present in the West Indies. The genus was monographed worldwide by Nishimura (1985). More recently Pedano (1996) examined the genus in eastern North America.