Macromitrium portoricense

Macromitrium portoricense R. S. Williams,
Bryologist 32 : 69. 1929.
Plants in wide, dense, rather thin mats on rocks; primary stems several cm. long, trailing, tomentose, bearing crowded, erect branches up to 1.5 cm. long, the branchlets short, 2-3 mm. long; stem-leaves very crispate when dry, erect-spreading when moist, 2 mm. long or less, oblong-lanceolate, keeled, rather broadly acute, the margins slightly crenulate above, plane or nearly so in the upper half; costa nearly percurrent to slightly excurrent, smooth on the back; leaf-cells incrassate, up to 10 fi long, nearly isodiametric to below the middle of the leaf, strongly mammillose on both sides, gradually changing into the elongate basal cells, which are narrowly linear except those near the costa and a single row of broad marginal cells near the base; basal cells bearing a considerable number of large, tubercle-like papillae; perichaetial leaves shorter and broader, the cells all more or less elongate, smooth except at the apex; no antheridia found; seta about 6 mm. long, smooth; capsules obovoid, the urn about 1.5 mm. long, smooth; calyptra without hairs, somewhat rough at the apex; stomata in 2 rows near the base of the capsule, superficial; peristome present (but in the specimens examined too old for description); spores smooth, 16-20 ju in diameter.
Type locality: On the road between Maricao and Monte Alegrillo, Puerto Rico, alt. 500-900 m. {E.G. Britton 2638).
Distribution : Known only from the type locality.