Crossidium

Plants in thin turfs or small cushions. Stem 1-10 mm, central strand present. Leaves evenly distributed or crowded, imbricate to slightly twisted when dry, lingulate, lanceolate to deltoid, 0.5-2.0 mm, 1-stratose, concave in distal half, base rectangular to ovate, margins entire, plane to recurved, apex obtuse, rounded or emarginate; costa excurrent as a whitish hair, in section hydroids present between the stereid and the guide cells, stereid band abaxial, filaments restricted to adaxial surface of costa, filament cells cylindric to subspheric, usually thin-walled, terminal cell cylindric to conic to subspheric, generally thin-walled, often papillose; cells of leaf base rectangular, firm-walled; medial and distal leaf cells quadrate to rectangular, firm-walled, sometimes thick-walled, smooth or with 1 to 8 papillae on either surface. Sexual condition dioicous or monoicous; perigonia budlike, leaves short and broad; perichaetia little or not differentiated. Seta 5-20 mm. Capsule cylindric to ovoid-cylindric, erect; annulus of 1-2 rows of vesiculose cells; operculum conic to rostrate, erect or inclined; peristome short and cribrose to long and twisted. Calyptra cucullate. Spores finely papillose, 9-22 µm.

Crossidium rosei R. S. Williams, described from Peru, was reported from North America by T. T. McIntosh (1989) from a specimen collected in British Columbia. This is a small sample containing plants of at least three pottiaceous species, including a fertile plant of Pterygoneurum. The type from Peru shows no relationship to the Canadian plants; i.e., Crossidium rosei is not part of the North American flora. Application of the name C. davidai Catcheside by M. J. Cano et al. (1992, 1993) to the Canadian specimen does not account for the lingulate and piliferous leaves of the American material.