Orthotrichum euryphyllum Venturi
Plants 1--5 cm. Stem leaves erect and loosely appressed when dry; oblong-lingulate, oblong-lanceolate, or ovate-lanceolate, 2.8--5 mm, obtuse or broadly acute; margins strongly revolute to just below apex, usually irregularly dentate at apex, rarely entire; distal laminal cells 7--18 µm wide, 1-stratose, with 1--3 small, conical papillae; basal laminal cells rectangular to short-rectangular, smooth. Sexual condition goniautoicous. Seta 1--1.5 mm. Capsule immersed when moist, barely to 3/4 emergent when dry; urn oblong to oblong-ovate, 1.5--2.5 mm, strongly 8-ribbed entire length; stomates immersed; peristome double; endostome segments 16, usually 1 cell wide, finely papillose; exostome teeth 8, sometimes splitting to 16, erect until old, then loosely reflexed, irregularly papillose, papillae tending to be confluent forming longitudinal striae. Calyptra 16-plicate with long beak, naked. Spores 10--17 µm.
Exposed tree roots, bases of trees along streams, also commonly on large boulders at the edges of streams and rivers, occasionally on rocks that are frequently inundated, rarely in aquatic habitats where usually on tree bases and rocks near streams; 500--2000 m; Alta., B.C.; Calif., Idaho, Nev., Oreg., Wash., Wyo.; Europe.
This species is distinguished from all others in the genus by the following combination of characters: (1) leaves often obtuse, the margins dentate near the apex, (2) calyptra plicate, the projecting edges papillose, otherwise smooth and naked, (3) 16 endostome teeth, and (4) stomates completely covered by the overarching subsidiary cells. I consider both O. epapillosum and O. euryphyllum to be ecological variants of this species.