Monographs Details: Plagiothecium
Authority: Buck, William R. 1998. Pleurocarpous mosses of the West Indies. Mem. New York Bot. Gard. 82: 1-400.
Description:Genus Description - Plants medium-sized or less often robust to small, in often lustrous, dark-green to yellow-green, sometimes whitish green, thin to dense mats. Stems creeping, 1-10 cm long, simple or irregularly branched, usually complanate-foliate, sometimes subjulaceous to julaceous; in cross-section with a single-layered hyalodermis, subtended by small firm- to thick-walled cells surrounding large thin-walled cells, central strand present or indistinct; pseudoparaphyllia foliose but rare and seemingly absent; axillary hairs with a single short brown basal cell and (2-)3 elongate hyaline distal cells. Stem and branch leaves similar, soft, imbricate to distant, erect or spreading, sometimes secund, little altered when dry, ovate, ovate-lanceolate, oblong-lanceolate or oblong-ovate, symmetric or often asymmetric, acute, acuminate or piliferous, often concave, occasionally undulate, strongly to scarcely decurrent; margins entire or serrulate to serrate at the extreme apex, plane or recurved below; costa short and double, one branch often reaching 1/3-1/2 the leaf length, rarely one branch poorly developed and costa appearing single, or costa sometimes lacking; cells linear, linear-flexuose or sometimes linear-rhomboidal, smooth or rarely with minute, granular, cuticular roughenings, often becoming shorter near the leaf apex and toward the insertion; alar cells differentiated, decurrent, in triangular or often auriculate and oval groups, in 1-8 vertical rows, spherical, oval, quadrate or rectangular, sometimes inflated. Asexual propagula often present from a stalked, branched gemmaphore, cylindrical or fusiform, 2-7-celled, uniseriate, clustered in leaf axils, sometimes on dorsal leaf surfaces, hyaline to light-green. Autoicous or dioicous. Perichaetia numerous at bases of stems; leaves moderately enlarged, convolute with spreading apices, oblong to oblong-lanceolate, acuminate; margins serrulate above, entire below, plane; costa mostly short and double or none; cells linear, smooth, becoming shorter and rectangular toward the insertion. Setae elongate, smooth, yellow, orange or reddish brown, straight, curved or rarely circinate, twisted; capsules erect to cernuous, straight or arcuate, yellow to reddish brown, cylindric or less often ovoid, occasionally striate or furrowed, often contracted under the mouth when dry and empty; exothecial cells quadrate to rectangular, thin- or thick-walled; annulus differentiated in 1-3 rows, deciduous, sometimes tardily so; operculum conic to rostrate, shorter than the urn; columella subglobular, short, ending below mid-urn; exostome teeth shouldered, bordered, on the front surface with a zig-zag median line, cross-striolate below, coarsely papillose above, rarely papillose throughout, trabeculate at back; endostome smooth or papillose, with a medium-high to high basal membrane, segments keeled, not or very narrowly perforate, cilia in groups of 1-3, nodulose, as long as or nearly as long as the segments, rarely rudimentary or lacking. Spores spherical or rarely ovoid, smooth or minutely papillose. Calyptrae cucullate, naked, smooth.
Discussion:Plagiothecium Bruch & Schimp. in Bruch, Schimp. & W. Gümbel, Bryol. Eur. 5(fasc. 48, Monogr. 1): 179. 1851; Stereodon sect. Plagiothecium (Bruch & Schimp.) Mitt., J. Linn. Soc., Bot. 4: 88. 1859.
Discussion. Plagiothecium is a genus of about 90 species predominantly occurring in the temperate zones, but reasonably represented in the tropics at higher elevations. The genus is characterized by mostly flattened plants with a well-developed alar region descending into narrow decurrencies. The stem has a 1-layered hyalodermis. The North American species were monographed by Ireland (1969), the Japanese species by Iwatsuki (1970), and the European species by Jedlicka (1948, 1950, 1961). Most recently the neotropical species were treated by Buck and Ireland (1989).