Wood Bristle Moss

Orthotrichum affine Brid. Muse. Recent
2 2 : 22. 1801.
Orthotrichum ajfine f. obtusa Grout, Moss Fl. N. Am. 2: 115. 1935.
Plants in rather small, loose tufts, dull green, 1-2 cm. high, branching freely above; leaves more or less closely imbricate when dry, oblong-lanceolate, acute to subacute, 3-4 mm. long, the'margins recurved to the apex; costa nearly or quite percurrent; upper leaf-cells irregularly rounded, isodiametric to slightly elongate, papillose, 12-15 u in diameter, the median basal cells smooth, elongate, subrectangular, rather thinwalled, subhy aline, the walls becoming slightly thickened and nodose with age, the marginal cells shorter; perichaetial leaves more or less obtuse; autoicous; seta about half the length of the capsule; capsules emergent to almost exserted, oblong-cylindric, strongly 8-ribbed and shrunken but not urceolate when dry and empty, the neck long and tapering ; calyptra slightly hairy ; stomata superficial, near the middle of the spore-sac; exothecial cells of the ribs strongly differentiated; annulus present, with 4 or
5 rows of small, thickwalled, transversely elongate cells below it; operculum conic-rostellate ; peristome-teeth 16, united in pairs, reflexed when dry, trabeculate and perforate above, papillose, the papillae sometimes arranged in lines, the segments 8, of two rows of cells, papillose, slender; spores 15-20 /x in diameter, maturing in early summer.
Type locality: Germany.
Distribution: On trees, rarely on rocks; the Rocky Mountains and westward; Kurope, Asia, and Africa; apparently rare in most parts of North America, frequent in Utah.