Monographs Details: Isopterygium
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 in thin to dense, light- to yellow-green, glossy mats. Stems creeping, simple or sparsely and irregularly branched; cortical cells as seen in section small and thick-walled, surrounding larger, thinner-walled cells; smooth rhizoids clustered on the underside of stems just below leaf insertions; pseudoparaphyllia filamentous, of 3-6 cells in 1 row or rarely 2 rows at base. Asexual reproductive bodies sometimes present, clustered on stems and branches, uniseriate, filamentous, simple or branched, green or brown, with papillose cells. Stem and branch leaves similar, rigid or flaccid, crowded and imbricate to remote, erect-spreading or squarrose, commonly complanate, sometimes contorted when dry, smooth, flat or somewhat concave, symmetric or asymmetric, non-decurrent or rarely with 1-2 cells decurrent, ovate or lanceolate, sometimes oblong, acute to acuminate; margins plane to erect, sometimes recurved at base, sermlate above the middle, mostly entire below, sometimes entire throughout; costa short and double, sometimes lacking; cells often smooth, linear or linear-fusiform, often flexuose, thin- to firm-walled, with walls not pitted or occasionally those of basal cells pitted; alar cells usually clearly differentiated, quadrate to rectangular, rarely transversely elongate. Autoicous or rarely dioicous. Perigonia scattered along the stems. Perichaetia at base of stems, with leaves oblong-lanceolate, gradually acuminate, and plane-margined. Setae elongate, smooth, straight to curved, usually twisted, yellow, brown, or red-brown; capsules inclined to cernuous, or sometimes erect, straight or curved when mature, brown to red-brown, cylindric, ellipsoidal, or ovoid, smooth or wrinkled at the neck and usually contracted below the mouth when dry; operculum conic to short-rostrate, shorter than the u m ; annulus none; exostome teeth cross-striolate below, papillose above, bordered, trabeculate at back; endostome with a low to high basal membrane, keeled segments, and cilia shorter than segments and in groups of 1-3, or sometimes lacking. Spores spherical to ovoid, smooth or minutely papillose. Calyptrae naked.
Isopterygium and Taxiphyllum have commonly been included in the genus Plagiothecium, which differs most obviously in having asymmetric, decurrent leaves. Isopterygium somewhat resembles Taxiphyllum, but the plants are generally smaller and have filiform pseudoparaphyllia. Both autoicous and dioicous species are k n o w n in Isopterygium, whereas all Taxiphyllum species presently known are dioicous. Other distinctive features include the smooth rhizoids arising below the leaf insertions, small and thick-walled outermost cortical cells, and capsules without an annulus.
Two genera have been segregated from Isopterygium: Isopterygiopsis and Pseudotaxiphyllum. For a comparison of those three genera, see Iwatsuki (1987). (Iwatsuki placed Isopterygium and its allies in the family Plagiotheciaceae.)