Monographs Details: Rhynchostegium
Authority: Sharp, Aaron J., et al. 1994. The Moss Flora of Mexico. Part Two: Orthotrichales to Polytrichales. Mem. New York Bot. Gard. 69 (2)
Description:Genus Description - Plants small to fairly robust, in loose, yellow- to dark-green mats. Stems prostrate or occasionally ascending, irregularly to subpinnately branched; branches horizontal to erect, terete- to complanate-foliate, attenuate. Leaves erect, appressed, or wide-spreading when dry, more spreading when moist. Stem leaves shghtiy concave, ± plicate, broadly ovate, oblong-ovate, or ovate-lanceolate, obtuse, acute, or acuminate, ± decurrent; margins reflexed at base, serrate to sermlate all around; costa ending at or beyond the midleaf, often in a dorsal spine; upper median cells fusiform, rhomboidal, or hnear, smooth, those of the acumen shorter and fusiform to linear; basal cells ± lax, linear to rectangular, occasionally with a row of laxly rectangular cells at the insertion; alar cells quadrate to rectangular, ± lax, occasionally bordered by a few rows of narrowly rectangular cells. Branch leaves generally smaller. Dioicous or monoicous. Setae elongate, red, smooth or papillose; capsules inclined to pendulous, ± curved, oblong-cylindric, with a short, tapered neck, generally contracted below the mouth when dry; annulus of 1-2 layers of transversely elongate or inflated cells; operculum rostrate from a conic base or more gradually rostrate; exostome teeth lance-subulate, red-brown, cross-striolate below, papillose above, trabeculate at back; endostome about as long as the teeth, consisting of lance-acuminate segments perforate along the keel arising from a high basal membrane and cilia 1-3, well developed, nodose or appendiculate. Spores smooth or nearly so.
Discussion:Rhynchostegium is presented here in a broad sense including taxa sometimes referred to Eurhynchium, Oxyrrhynchium, Steerecleus, and Platyhypnidium in addition to Rhynchostegium in a narrow sense. These genera have in common a rostrate operculum as well as costae often ending in a dorsal spine. Oxyrrhynchium has been used for species with broad leaves, dioicous inflorescences, and rough setae. Platyhypnidium is a convenient designation for aquatic, autoicous species. Eurhynchium is sometimes reserved for terrestrial species with short apical cells, m u c h like Platyhypnidium in most respects. Rhynchostegium has been a name of uncertain application. In the literature ofthe Americas at least, it has generally been used for species with more or less complanate leaves ending in a long acumen and having long apical ceUs. Robinson (1987) has provided the genus Steerecleus for species that lack short apical cells and have poorly differentiated alar ceUs and smooth setae.