Physcomitrella Bruch & Schimper, Bryologia Europaea. 1: 13 (fasc. 42. Mon. 1.). 1849.
[Latin -ella, diminutive, resembling a small Physcomitrium]
Plants small, to 0.5 mm, green, scattered to gregarious. Stems short, 3--3.5 mm, simple or branched, rhizoids light brown, smooth. Leaves somewhat crisped when dry, erect-spreading when moist, 2--2.5 × 0.6--1 mm, margin serrulate distally, entire proximally; costa single; cells thin-walled, smooth, proximal cells rectangular, distal cells short-rectangular to rhombic with narrow ends. Sexual condition paroicous. Seta erect, to 0.2 mm. Capsule erect, immersed, symmetric, brown, globose and apiculate, apiculus to 0.2 mm, smooth, wrinkled upon aging, to 0.8 mm, annulus none; peristome lacking; exothecial cells very thin-walled, translucent at maturity, irregular in shape; stomata with single guard cell, restricted to base of capsule, superficial. Operculum not differentiated, dehiscence irregular. Calyptra short, to 0.2 mm, covering apiculus of capsule only, smooth. Spores spherical to slightly elliptical, densely papillose to slightly spinulose, light brown.
Species 2 (2 in the flora): North America, c and n Europe, Asia (China, Japan), Africa, Australia.
Physcomitrella is distinguished from other species of Funariaceae by the immersed capsule with irregular dehiscence, and the thin-walled, translucent exothecial cells. The generic name implies a resemblance to Physcomitrium, which is named, however, for its large calyptra, unlike that of Physcomitrella.
Crum, H. A. and L. E. Anderson. 1955. Bryologist 58: 1--5. Crum, H. A. and L. E. Anderson. 1981. Mosses of Eastern North America. Volume 1. New York.