Monographs Details: Trichosteleum
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 moderately robust, in somewhat lustrous, ± soft, mostly yellow-green to golden, thin, often extensive mats. Stems creeping, freely but irregularly branched, the branches sometimes obscurely complanate-foliate; in cross-section with small thick-walled colored cells surrounding larger thinner-walled cells, central strand absent; pseudoparaphyllia mostly none; axillary hairs with 1(-2) short brown basal cells and 1 to several elongate hyaline distal cells. Stem and branch leaves similar, erect-spreading or falcate-secund, lanceolate to ovate-lanceolate, acute to acuminate-subulate, concave; margins subentire to serrate above, plane or sometimes recurved; costa short and double or absent; cells linear, unipapillose, usually thick-walled and porose, sometimes becoming shorter in the extreme apex, becoming thicker-walled and more conspicuously porose toward the insertion; alar cells greatly enlarged and inflated, oblong, often colored. Asexual propagula ? none. Autoicous. Perichaetial leaves erect, mostly lanceolate, acuminate; margins often serrate, plane; costa mostly none; cells linear, mostly smooth, thick-walled, porose, becoming laxly rectangular toward the insertion; alar cells not differentiated. Setae elongate but relatively short, slender, often roughened above, occasionally smooth, reddish, curved just below the urn; capsules suberect to pendent, small, ± asymmetric, ovoid to cylindric; exothecial cells mostly subquadrate, strongly collenchymatous. often bulging at base of urn from protruding stomata and auxiliary cells; annulus not differentiated; operculum obliquely and slenderly long-rostrate; peristome double, exostome teeth narrowly triangular, shouldered, bordered, on the front surface with a zig-zag median line or a median furrow, cross-striolate below, coarsely papillose above, trabeculate at back; endostome with a high basal membrane, segments broad, keeled, perforate, almost as long as the teeth, cilia usually single. Spores spherical, papillose. Calyptrae cucullate, naked or very rarely sparsely hairy, smooth, roughened, or ridged above.
Discussion:Trichosteleum Mitt., J. Linn. Soc., Bot. 10: 181. 1868; Sematophyllum sect. Trichosteleum (Mitt.) Mitt., J. Linn. Soc., Bot. 12: 476, 492. 1869; Rhaphidostegium sect. Trichosteleum (Mitt.) Besch., Ann. Sci. Nat. Bot. VI, 3: 250. 1876.
Discussion. Trichosteleum is separated from many of the other genera of Sematophyllaceae with collenchymatous exothecial cells and inflated, colored alar cells by unipapillose laminai cells. Although often defined by a furrowed exostome, this is not a consistent feature, even for the West Indian species. The type species, T. fissum Mitt, from Samoa, lacks a furrowed exostome. Trichosteleum may be polyphyletic as it is essentially a one-character genus. Indeed, in some species, such as T. microstegium, the papillae are inconspicuous and not over every cell. This is in contrast to species such as T. sentosum in which the papillae are even visible with a dissecting microscope. I (Buck, 1983c) reviewed the Antillean species.