Streamside Orthotrichum Moss

Orthotrichum rivulare Turner, Muse. Hib. 96. 1804
Plants blackish-green, aquatic, in floating or submerged tufts; stems 2-4 cm. long, sparingly branched above; leaves loosely imbricate when dry, oblong-lingulate, obtuse, often irregularly toothed at the apex, ± 3 mm. long, the margins revolute to near the apex, decurrent; costa strong, ending shortly below the apex ; leaf-cells except at the base papillose on both sides with low, simple papillae, the upper rounded, rather irregular, nearly isodiametric, 10-12 p in diameter, the basal rectangular; autoicous; seta short; capsules immersed to emergent, the short neck sometimes abruptly contracted to the seta, 8-ribbed, oblong-ovoid to ovoid, strongly contracted below the mouth when dry and empty, the urn about 2 mm, long, dark red at the mouth ; calyptra naked, deeply plicate ; exothecial cells of the ribs well differentiated ; stomata immersed, near the base of the capsule; operculum conic-apiculate ; peristome double, the 16 teeth in pairs, recurved when dry, papillose, the papillae tending to fuse into irregular groups, the 16 segments slender, 8 about the length of the teeth, the alternating shorter, smooth, more or less appendiculate; spores 15-18 p in diameter, maturing in spring.
Type locality : Europe.
Distribution: On rocks, or occasionally on wet wood or the bases of trees; apparently common in parts of California; Oregon; Washington; Idaho.