1. Orthotrichum affine Schrader ex Bridel, Muscol. Recent. 2(2): 22. 1801.
Plants to 3 cm. Stem leaves erect-appressed and straight when dry, ligulate, elongate- to ovate-lanceolate, 2-4 mm; margins recurved-revolute to just below apex, entire; apex acute; basal laminal cells long-rectangular to elongate, walls thick, nodose; distal cells 9-13 µm, 1-stratose, papillae 2 or 3 per cell, 2-fid, low. Specialized asexual reproduction absent. Sexual condition gonioautoicous. Seta 1-2.2 mm. Capsule 1/2 emergent to short-exserted, long-cylindric when mature, cylindric and constricted along entire length when old and dry, 1.6-2.5 mm, strongly 8-ribbed 2/3 capsule length; stomata superficial; peristome double; prostome absent; exostome teeth 8, erect when mature, reflexed to reflexed-recurved when old, coarsely and obscurely papillose or sometimes papillose-reticulate, ; endostome segments 8, rarely 16, well developed, , of 2 rows of cells, papillose. Calyptra conic-oblong, smooth, hairs few, papillose. Spores 15-18 µm.
Deciduous trees, shaded rock, shaded forests near stream beds, canyons, mountains; low to high elevations (0-3000 m); Alta., B.C.; Calif., Colo., Idaho, Mont., Oreg., Utah, Wash.; Europe; Asia; n Africa.
Orthotrichum affine, a species confined to western North America in the flora area, is best recognized by: superficial stomata; cylindric, strongly ribbed, almost exserted capsules; a well-developed but not stout endostome; and a calyptra that is only sparsely hairy.