Orthotrichum immersum Bridel; O. pallens var. immersum (Bridel) Müller Hal.

Plants 0.3-1 cm. Stem leaves loosely erect-appressed and slightly incurved when dry, oblong-lanceolate to broadly lanceolate, 1.6-3 mm; margins recurved to near apex, entire or crenulate at apex; apex narrowly obtuse, acute, or apiculate; basal laminal cells rectangular, walls thin, not nodose; distal cells 9-14 µm, 1-stratose, papillae 2 or rarely 3 per cell, conic, lo w. Specialized asexual reproduction occasional, by gemmae on leaves. Sexual condition cladautoicous. Seta 0.5-1.5 mm. Capsule emergent to barely exserted, oblong to oblong-cylindric, 1-2.5 mm, strongly 8-ribbed, narrowly cylindric and contracted along entire length when old; stomata immersed, ; peristome double; prostome absent; exostome teeth 8, erect, reflexed or recurved-reflexed with age, finely papillose, densely papillose, or papillose-striate; endostome segments 8 or 16, well developed, of 1 or 2 rows of cells, smooth or finely papillose. Calyptra conic-oblong, smooth, naked or sparsely hairy, hairs smooth. Spores 10-20 µm.

Varieties 9 (3 in the flora): North America, Mexico, Europe.

Orthotrichum pallens is distinguished by the immersed stomata that are scarcely covered by thin-walled subsidiary cells. The peristome is double with a well-developed endostome of 16 (or eight) segments that remains intact until the capsule is quite old. Gametophytically, O. pallens is distinguished by narrowly obtuse, oblong-lanceolate leaves, and an autoicous sexual condition.