1. Thelia asprella (Schimper) Sullivant in A. Gray, Manual ed. 2. 660. 1856.
Leskea asprella Schimper in P. Bruch and W. P. Schimper, Bryol. Europ. 5: 136. 1850; Hypnum hirtellum var. furcatum Müller Hal.
Stems creeping, densely and regularly 1-pinnate, often densely tomentose, branches simple; paraphyllia not seen; pseudoparaphyllia filamentous. Stem and branch leaves ± similar, 0.8-1 mm; margins plane throughout or erect to somewhat incurved basally, plane distally, ciliate basally, ciliate-papillose distally; apex broadly acute to obtuse, acumen spreading-piliferous, occasionally long-apiculate; laminal cells rhombic nearly throughout, 12-20 × 8-12 µm, papillae usually 3-6-branched. Seta 0.8-1.2 cm. Capsule 2-2.5 mm; operculum 1-1.3 mm. Calyptra 2-3 mm. Spores 6-10 µm.
Tree trunks, rotting stumps, humus, soil at base of trees, over rock, on ground; low to moderate elevations (20-800 m); Ont., Que.; Ala., Ark., Conn., Del., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Tex., Vt., Va., W.Va., Wis.
Thelia asprella is a fairly small species that usually grows in large, dense mats at the base of trees. Thelia asprella and T. hirtella are nearly identical in aspect; both species have terete-foliate, regularly branched, densely radiculose stems, and piliferous leaves. Thelia hirtella differs from T. asprella most clearly in having unbranched laminal cell papillae; in addition, the leaves in T. hirtella are dimorphic with stem leaves much larger and more densely ciliate than the branch leaves. Thelia lescurii is a larger plant than T. asprella that nearly always grows on soil or over rocks. In the field, T. lescurii can often be distinguished from T. asprella because its short-apiculate leaves give the plants a smoothly imbricate appearance. In T. asprella, the piliferous apices are often spreading, giving the plants a ragged appearance.