Orthotrichum psilocarpum Sullivant
Plants 2--4 mm. Stem leaves loosely-appressed when dry, ovate-lanceolate to oblong-lanceolate, 1--2.2 mm, narrowly obtuse to broadly acute, sometimes with small apiculus; margins revolute nearly to apex, entire except for denticulate apex on some leaves; distal laminal cells 9--14 µm wide, 1-stratose, with 2--4 small, conical papillae; basal laminal cells, broadly rectangular, non-nodose. Sexual condition autoicous. Seta less than 1 mm. Capsule immersed to 1/2 emergent; urn oblong to ovate-oblong, 0.8--1.4 mm, wrinkled to lightly 8-plicate; stomates immersed, at middle or distal portion of capsule; peristome single; endostome segments usually absent or if present 8, rudimentary, smooth; exostome teeth 16, erect or recurved. Calyptra oblong, smooth. Spores 13--20 µm.
Trunks of deciduous trees in open, dry woods and along roadsides, rarely on Juniperus associated with habitation along streams; 10--1000 m; Ala., Ark., Conn., D.C., Fla., Ga., Ill., Ind., Kans., Ky., La., Md., Mass., Mich., Miss., Mo., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., S.C. Tenn., Texas, Va., W.Va.
Orthotrichum pusillum is distinguished by its smooth, oblong capsule, which is sharply contracted to the seta, 16 peristome teeth, which are erect or recurved when old, some leaves of each plant having 1--4 small denticulations at the apex, and distal leaf cells 9--14 µm in width. The leaf cells are smaller than those of O. pumilum and in longitudinal rows, but they are larger, with thinner walls, than those of O. ohioense. To identify sterile material: O. pusillum---denticulate leaf apex that may be narrowly obtuse or acute, and leaf cells 9--14 µm with thin walls; O. pumilum---apiculate leaf apex that is normally acute and entire, and leaf cells 14--20 µm, with thin walls; and O. ohioense---obtuse leaf apex, which is never apiculate or denticulate, and leaf cells 8--10 µm, with thick walls.