Dale H. Vitt
Plants small, slender, dull to bright green, in loosely interwoven, straggly mats. Stems prostrate, creeping, and irregularly branched; branch foliage similar to that of stem; axillary hairs 4--6-celled, distal cell obtuse, pale brown; juvenile branch leaves narrowly acute. Stem leaves ovate to ovate-lanceolate, acute to narrowly obtuse, concave, imbricate and ± subsecund, little decurrent; margins entire, subentire, to serrulate in distal 1/2, costa slender, reaching 1/3--2/3\x leaf length, ending without a spine; basal laminal cells quadrate to subquadrate, shorter at margins, in many rows, walls thin; laminal cells rhombic to oblong-rhombic, thin-walled, smooth. Branch leaves similar to stem leaves. Sexual condition autoicous; perichaetial leaves abruptly acuminate, erect to flexuose from sheathing base. Seta reddish, smooth. Capsule erect, narrowly elliptic to oblong, symmetric; annulus of 3--4 rows of small, brown cells, persistent; operculum long-rostrate; peristome double, of 16 short, slender, unequally 2-fid segments partially fused to inconspicuous basal membrane; exostome of 16, very short, blunt, partially fused teeth. Calyptra naked. Spores 14--21 \um, finely roughened.
Species 1 (1 in the flora): North America,
Clasmatodon has been variously placed in the Fabroniaceae or the Myriniaceae, but molecular data strongly suggest a position in the Brachytheciaceae as a small, epiphytic, monotypic genus with a reduced peristome.
Clasmatodon parvulus (Hampe) Sullivant in A. Gray, Man.
Leskea parvula Hampe, Linnaea 13: 46. 1839; Clasmatodon parvulus var. rupestris Lesquereux & James
Stems to 1(--2) cm, branches to 2(--5) mm. Stem leaves 0.4--0.7 x 0.3--0.5 mm; mid-leaf cells 18--30 X 8 --10 \um. Seta 2--5 mm. Capsule 0.7--1 mm.
Tree trunks and bases of trees, often in flood plain forests, or more rarely on calcareous rocks; 0--400 m; Ala., Ark., Fl., Ga., Ill., Ind., Ky., La., Md., Miss., Mo., N.C., Ohio, Okla., Pa., S.C., Tenn., Tex., Va., W.Va.
parvulus is an inconspicuous moss forming small, slender, straggly
mats on tree trunks in the southestern