Monographs Details: Platygyrium
Authority: Sharp, Aaron J., et al. 1994. The Moss Flora of Mexico. Part Two: Orthotrichales to Polytrichales. Mem. New York Bot. Gard. 69 (2)
Family:Hypnaceae
Scientific Name:Platygyrium
Description:Genus Description - Plants of small to medium size, in low, dark- or yellow-green to red-brown, glossy mats. Stems creeping, adhering substrate by dense rhizoids, in section dorsiventrally flattened and elliptic, without a central strand, pinnately to irregularly branched; branches erect or ascending, sometimes curved, usually bearing brood branchlets in upper leaf axils. Stem and branch leaves similar (the stem leaves somewhat broader and less concave), usually appressed when dry, erect-spreading when moist, rarely homomallous, concave, ovate- or oblong-lanceolate, short- or long-acuminate; margins entire or nearly so, usually reflexed or recurved; costa short and double or none; upper cells linear-rhomboidal, shorter near the apex, smooth; alar cells subquadrate to rectangular and relatively large in several rows at basal angles. Dioicous. Perichaetial leaves ovate- to oblong-lanceolate, loosely sheathing, with ± spreading tips, not or slightly plicate. Setae smooth; capsules erect and symmetric or slightly inclined, cylindric; annulus persistent, consisting of several rows of cells; exothecial cells subquadrate to oblong-hexagonal, with walls thin or somewhat thickened; operculum obliquely conic-rostrate; exostome teeth rather deeply inserted, lance-subulate, pale-yellow to yellow-brown, papillose in lines or cross-striolate below, papillose or nearly smooth above, widely bordered, trabeculate at back; endostome free, shorter and usually darker than the exostome teeth, smooth, with a very low basal membrane, nearly linear, keeled, and sht or perforate segments, and cilia mdimentary or lacking. Spores minutely roughened. Calyptrae naked.

Discussion:

Distinctive features of the genus are the axillary brood branchlets and leaves erect, with relatively large subquadrate alar cells and usually recurved margins. The endostome consists of a very low basal membrane, nearly linear segments, and cilia mdimentary (or none).