Neckera commutata Müller Hal., Bot. Zeitung (Berlin) 15: 385. 1857; Fabronia donnellii Austin; Meiotheciopsis commutata (Müller Hal.) W. R. Buck; Meiothecium tenerum Mitten

Stems with branches ascending. Leaves slightly concave, 0.6-1.1 × 0.2-0.4 mm; alar cells short-oblong, yellow, supra-alar cells quadrate, not inflated, unpigmented; distal laminal cells long-rhomboidal to long-hexagonal, walls thick. Capsule 0.7-1.2 mm, slightly or not contracted below mouth; annulus absent; peristome bone white when dry, ± translucent when moist; exostome teeth with external surface with straight median line, not furrowed, not cross striolate, lamellae conspicuous, internal surface scarcely projecting; endostome fragile, basal membrane very low or absent, appearing absent in deoperculate capsules, segments linear, almost as long as exostome teeth, ± keeled, not perforate, finely papillose, sometimes fugacious, cilia absent. Spores 25-27 µm.

Capsules mature winter. White sand evergreen oak scrub forests, trunks and large branches (including canopy) of Quercus; low elevations; Fla.; Mexico; West Indies; Central America; South America.

Donnellia commutata is common in oak scrub of north central Florida, but has been mostly overlooked because of its sympatry with and morphological similarity to Sematophyllum adnatum, one of the great weedy mosses. Donnellia commutata may be distinguished satisfactorily only when fertile by its shorter setae, white peristome (when dry), and rather smooth exostome teeth. The endostome often appears absent because the segments break off shortly after the loss of the operculum. However, the endostome can be easily demonstrated by the dissection of mature, operculate capsules.