Isopterygium Mitten, J. Linn. Soc. Bot. 12: 21. 1869.
[Greek iso, equal, and pteron, winged]
Robert R. Ireland
Plants small to medium-sized, in thin to dense, light- to yellowish-green glossy mats. Stems 4--5 cm, creeping, simple or sparingly and irregularly branched, cortical cells small and thick-walled in cross section, surrounding larger, thinner walled cells, central strand usually absent; rhizoids smooth, on ventral surface of stems and branches just below juncture of leaves; axillary hairs with one brownish short-rectangular cell and one hyaline elongate apical cell; filamentous pseudoparaphyllia present, of 3--6 cells in 1 row or rarely with 2 rows at base. Leaves of stems and branches similar, rigid or flaccid, crowded and imbricate to remote, erect-spreading or squarrose, commonly complanate-foliate, sometimes wrinkled and contorted when dry, smooth, flat or somewhat concave, symmetric or asymmetric, nondecurrent or rarely with 1--2 cells decurrent, ovate or lanceolate, acute to acuminate; margins plane to erect, sometimes recurved at base, serrulate above the middle, mostly entire below, sometimes entire throughout; costa short and double, sometimes lacking; cells often flexuose, thin to firm-walled, linear-fusiform, smooth, with walls not pitted or occasionally those of basal cells pitted; alar cells usually clearly differentiated, quadrate to rectangular, rarely transversely elongate. Specialized asexual reproduction sometimes present on stems and branches, of uniseriate, often branched, filamentous, multicellular bodies with papillose cells. Sexual condition autoicous or rarely dioicous; perigonia scattered along stems; perichaetia at base of stems, leaves oblong-lanceolate, gradually acuminate, margins plane. Seta solitary, yellow, brown or reddish brown, 0.5--3 cm, usually twisted, straight to curved, smooth. Capsule inclined to cernuous, sometimes erect, straight or arcuate when mature, brown to red-brown, cylindric, ovoid or ellipsoid, smooth, usually contracted below mouth and sometimes wrinkled at neck when dry; operculum conic to short-rostrate, shorter than urn; annulus lacking; peristome double, exostome teeth cross-striolate below, papillose above, bordered, trabeculate at back; endostome with high to low basal membrane, segments keeled, cilia shorter than segments, in groups of 1--3, sometimes lacking. Calyptra cucullate, smooth, naked. Spores spherical to ovoid, smooth or minutely papillose.
Species 120--140 (2 in the flora) but many will undoubtedly be synonymous with other taxa after a worldwide revision; North America, Mexico, West Indies, Central America, South America, Europe (Italy), Asia, Africa, Pacific Islands, Australia.
Plants of this genus occur predominately in terrestrial habitats at low elevations in the subtropics and tropics.
SELECTED REFERENCES
Ireland, R. R. 1969. A taxonomic revision of the genus Plagiothecium for North America, north of Mexico. Natl. Mus. of Canada, Natl. Mus. of Natural Sci., Publ. in Bot., No. 1: 1--118. Ireland, R. R. 1992. The moss genus Isopterygium (Hypnaceae) in Latin America. Tropical Bryology 6: 111--132. Iwatsuki, Z. 1970. A revision of Plagiothecium and its related genera from Japan and her adjacent areas, I. J. Hattori Bot. Lab. 33: 331--380. Iwatsuki, Z. 1987. Notes on Isopterygium Mitt. (Plagiotheciaceae). J. Hattori Bot. Lab. 63: 445--451. Iwatsuki, Z. and M. R. Crosby. 1979. Lectotypification of the genus Isopterygjum Mitt. J. Hattori Bot. Lab. 45: 389--393. Redfearn, P. L., Jr. 1956. Biometric analysis of the stem leaf variation of the Plagiothecium micans complex in southeastern United States. Bryologist 59(4): 256--262.
