Monographs Details: Pilosium
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:Plagiotheciaceae
Scientific Name:Pilosium
Description:Genus Description - Plants moderately robust, in glossy, green or yellow-green mats. Stems creeping, freely and irregularly branched, showing small, thick-walled cells surrounding an inner tissue of large, thin-walled cells and no central strand; pseudoparaphyllia filamentous. Brood bodies none. Stems and branch leaves similar. Lateral leaves wide-spreading and strongly complanate, often decurved at the tips when dry, asymmetric, oblong-ovate, obtuse to acute, non-decurrent; margins broadly inflexed on 1 side below, entire or sometimes serrulate near the apex; costa short and double or none; upper cells linear-flexuose, thin-walled, chlorophyllose, smooth; alar cells large, oblong, hyaline or brownish. Dorsal leaves erect-appressed, somewhat smaller, nearly symmetric, with fewer, smaller, ± quadrate alar cells. Autoicous. Perichaetial leaves ovate-lanceolate and subulate, deeply erose, with linear cells. Setae elongate, slender, smooth; capsules cernuous, small, oblong-cylindric, smooth; annulus none; operculum obliquely rostrate; exothecial cells collenchymatous; exostome teeth cross-striolate below, papillose above, not furrowed, bordered, trabeculate at back; endostome papillose, with a high basal membrane, keeled and perforate segments (not exceeding the teeth), and single cilia shorter than the segments. Spores spherical, papillose. Calyptrae cucullate, smooth, naked.

Discussion:

The genus, treated in some detail by Grout (1945), has in the past been included in the Plagiotheciaceae and in the relationship of Stereophyllum. It has a considerable resemblance to some of the genera of the Hookeriaceae, because of asymmetric, complanate leaves and collenchymatous exothecial cells. It resembles, for example, some species of Lepidopilum, but the peristome is not at all like that of a Lepidopilum. It has some of the features of a Rhynchostegiopsis, except that the teeth are not furrowed. The gametophytic and sporophytic characters straddle the boundary between the Hookeriaceae Daltoniaceae, as estabhshed by Crosby (1974), but whether pseudoparaphyllia are allowable in the Hookeriaceae remains a question. (See also Elharveya and Curviramea.) The Hookeriaceae in the broad sense presented here are admittedly heterogeneous and thus allow for at least temporary placement of Pilosium in this general relationship (see Buck & Ireland, 1985).

The genus consists of a few tropical American species, probably all falling within the variability of a single species.