Sessile Pterygoneurum Moss

Pterygoneurum subsessile is an abundant moss in the arid West, often occurring with P. ovatum. In some specimens, the perigoniate plants appear separate, but this species and doubtless others are apparently occasionally rhizautoicous. Following the reasoning of R. T. Wareham (1939), var. henrici is placed with the typical variety. The characters associated with P. californicum (H. A. Crum 1967) are poor: the spores are finely papillose, the leaf cells do have weak collenchymatous thickenings, and the calyptra is long-mitrate.

Leaves with distal lamina smooth; awn smooth or sharply serrulate; lamellae 10-12 cells in height, not lobed, sometimes bearing fila-ments. Capsule stegocarpous (or stegocarpous but bursting irregu-larly), immersed to emergent, short-ovoid, annulus present, operculum cells in straight rows; eperistomate. Calyptra mitrate.

Plants 2–4 mm high, grayish green to yellowish green, gregarious or in thin tufts. Stems erect, simple or occasionally branched at the base. Leaves appressed when dry, weakly erect-spreading when moist, oblong ovate to ligulate or elliptic, strongly concave, 2–3 mm long with the awn; margins entire or serrulate at or near the base of the awn, plane or weakly incurved; costa rather stout, excurrent, ending in a long awn, nearly twice as long as the leaf length, denticulate; with 2–4 rows of green lamellae on the ventral side of costa; upper leaf cells quadrate to rounded hexagonal, 10–14 µm in diameter, moderately thick-walled, smooth or with simple or blunt C-shaped papillae; basal cells rectangular, 23–40 µm x 13–16 µm, thin-walled, smooth. Setae 0.3–0.5 mm long; capsules immersed, subhemispheric to ovoid; annuli none; opercula conic-rostrate, with a short, straight beak; peristome teeth absent. Calyptrae mitrate, smooth. Spores 35–38 µm in diameter, brownish, finely papillose.

Distribution: China, Mongolia, Russia, Central Asia, Europe, North America, and northen Africa.

Habitat: on soil or thin soil over rocks.

Gymnostomum subsessile Bridel, Muscol. Recent., suppl. 1: 35. 1806