Monographs Details: Pleurozium
Authority: Sharp, Aaron J., et al. 1994. The Moss Flora of Mexico. Part Two: Orthotrichales to Polytrichales. Mem. New York Bot. Gard. 69 (2)
Family:Hylocomiaceae
Scientific Name:Pleurozium
Description:Genus Description - Rather robust plants in deep, light-green or yellowish, ± shiny mats. Stems erect-ascending, pinnately branched; branches loosely julaceous, blunt or tapered; paraphyllia none. Leaves loosely imbricate, very concave, obscurely wrinkled-plicate when dry, broadly oblong-ovate, rounded at the apex and generally appearing to be recurved-apiculate because of abmptly incurved margins, somewhat decurrent; margins plane or reflexed near the base, broadly incurved above, crenulate to sermlate at the apex; costa short and double; upper cells linear, smooth; cells at the insertion thick-walled, porose, and orange, the alar cells short-oblong with thick, orange walls, in rather small, triangular, often concave groups. Branch leaves shorter and narrower. Perichaetial leaves erect, oblong-lanceolate, acuminate. Capsules strongly inclined to horizontal, curved, oblong-cylindric from a tapered neck, smooth; annulus none; operculum conic or convex-conic, acute; exostome teeth brown or brownish-yellow, very finely reticulate throughout (or only indistinctly transversely papillose-striolate below), bordered; endostome pale-brownish, finely papillose, with a high basal membrane, keeled and gaping segments, and well-developed cilia in groups of 2-3.

Discussion:Pleurozium has sometimes been placed in the Entodontaceae because of deeply concave, imbricate leaves and tumid stems and branches. For the same reasons, and because of crowding of leaves at more or less cuspidate branch tips, the genus has also been subordinated to Calliergonella, and the leaf stmcture is superficially somewhat like that of C. cuspidata. The shape of the capsule and its inclined to horizontal posture ill conform to the Entodontaceae and suggest a relationship to the Brachytheciaceae, but the chromosome number and minutely areolate sculpturing of exostome teeth show a more likely relationship to Rhytidiadelphus, and the Hylocomium-like appearance of gametophytes and sporophytes signifies a relationship to the Hylocomiaceae.