Orthotrichum coulteri Mitten; O. cylindrocarpum Lesquereux; O. tenellum var. coulteri (Mitten) Grout; O. tenellum var. cylindrocarpum (Lesquereux) L. F. Koch

Plants 0.3-1 cm. Stem leaves stiff, erect-appressed when dry, ligulate to lanceolate-oblong, polymorphic, 1.3-2.6 mm; margins revolute to below apex or sometimes broadly reflexed distally, entire, sometimes serrulate in apex; apex obtuse to broadly acute, apiculate, ; basal laminal cells broadly rectangular, walls thin, not nodose; distal cells 8-13 µm, 1-stratose, papillae 2 or 3 per cell, conic, low. Specialized asexual reproduction by gemmae on abaxial surface of leaves. Sexual condition cladautoicous or rarely gonioautoicous. <Vaginula with hairs absent>. Seta to 2 mm. Capsule 2/3 emergent to short-exserted, cylindric to cylindric-elliptic when mature, 1.3-2 mm, strongly 8-ribbed entire length, not constricted below mouth; stomata immersed, ; peristome double; prostome absent; exostome teeth 8, rarely splitting to 16, erect when mature, reflexed when old, papillose; endostome segments 8, rarely 16, well developed, of 2 rows of cells, finely papillose. Calyptra conic-oblong, smooth, naked or sparsely hairy, hairs sometimes papillose by projecting walls. Spores 11-18 µm.

Trunks of deciduous trees in dry, open areas, rock; low to high elevations (100-2000 m); B.C.; Calif., Nev., Wash.; Europe; n Africa; Atlantic Islands (Azores, Canary Islands).

Orthotrichum tenellum is the only western species with deeply immersed stomata, blunt leaves, and oblong-cylindric capsules; its small size distinguishes it from other Californian species found on trees. The leaves are spreading to wide-spreading in the distal portions of the branches.