Pterigynandrum trichomitrion Hedwig, Sp. Musc. Frond., 82, plate 16, figs. 1-6. 1801; Leptodon trichomitrius (Hedwig) Sullivant & Lesquereux; L. trichomitrius var. floridanus (Lindberg) Grout; L. trichomitrius var. immersus (Sullivant & Lesquereux) Sullivant

Stem and branch leaves lanceolate, ovate-lanceolate, broadly ovate-lanceolate, oval, or deltoid, 1-3 × 0.5-1.2 mm; costa single, weak, 1/4-3/4 leaf length, or double, short; laminal cells fusiform to linear, 4-8:1; medial cells 25-80 × 5-11 µm. Sexual condition autoicous, often gonioautoicous. Seta 0.4-3.9 mm. Capsule immersed to exserted, 1-2.3 × 0.4-1 mm; operculum 0.5-1.1 × 0.3-0.6 mm; exostome teeth smooth, minutely papillose, or occasionally granulose. Spores 18-30 µm.

Capsules mature winter. Epiphytic, boles of hardwood trees, rock, bark of evergreen trees, shaded, relatively humid areas, along streams; low to high elevations; Ont.; Ala., Ark., Conn., Del., D.C., Fla., Ga., Ind., Ky., La., Md., Mass., Mich., Miss., Mo., N.J., N.Y., N.C., Ohio, Okla., Pa., S.C., Tenn., Tex., Vt., Va., W.Va., Wis.; Mexico; South America; e Asia; e Australia.

Immersed capsules (with short setae) are very common in Forsstroemia trichomitria in the states bordering the Gulf of Mexico. However, from Virginia northward, capsules are nearly always either emergent or exserted. The two North American species of Forsstroemia rarely may form hybrids that have intermediate features of medial laminal cell length, costal length, frequency of single costae, seta length, post-fertilization perichaetial leaf length, and peristome appearance (L. R. Stark 1987). The secondary stems are usually subpinnate.