Oefv. K. Svensk. Vet. Ak. Foerh. 23: 549. 1867.
Orthotrichum jamesianum Sull. ex James in Watson, Bot. U.S. Geol. Expl. 40th Parall. Prof. Pap. Eng. Dept. U. S. Army 18: Vol. 5: 401. 1871. -- Orthotrichum jamesii Sull. ex Kindb., Eur. N. Am. Bryin. 2: 308. 1897. -- nom. illeg. -- Orthotrichum cupulatum var. jamesianum (Sull. ex. James in Watson) Lawton, Moss Fl. Pac. NW. 221. 1971.
Orthotrichum subsordidum Kindb. ex Mac., Cat. Can. Pl. 7: 233. 1902.
Plants erect in small dark green to glaucous green tufts, to 3 cm high. Leaves spreading when moist but, when dry, rather rigidly erect with apices laterally twisted. Leaves to 2.5 mm long, about 4: 1, ligulate-lanceolate to elliptic-lanceolate, broadest near the middle, with obtuse apices. Median laminal cells isodiametric with rounded lumens, thick walled with strong corner thickening, to 9 µm wide, very high pluri-papillose with papillar salients forked and almost as high as the leaf thickness. Basal juxtacostal cells pellucid and rectangular, 1.5–3: 1, to 12 µm wide with lateral walls straight and thin. Basal juxtamarginal cells isodiametric, pellucid and relatively thin-walled, to 20 µm wide. Margins recurved from base to near the apex, entire to papillose crenate, occasionally with a few serrulations at the extreme apex. Costa ending within about ten cells of apex, not situated in a keel. Costa cross-section homogeneous, at mid-leaf 3–4 cells thick with about 8 cells on abaxial perimeter. Axillary hairs with one basal brown cell, not offset from leaf insertion, of essentially uniform diameter from base to apex, with the medially inserted ones to 8 cells and 300 µm long but with the lateral ones much shorter. Rhizoids sparse and restricted to base of plant, smooth and very thick-walled, red-brown, to 25 µm in diameter at base, sparingly branched. Stem cross-section rounded pentagonal, without a central strand, with hyaline inner corticals and with 1–2 layers of somewhat thicker-walled, red brown outer cortical cells.
Autoicous with perigonia in leaf axils near the perichaetia. Perichaetial bracts similar to the vegetative leaves. Capsule immersed to slightly emergent on a yellow to yellow brown, smooth and erect seta of about 1 mm in length. Urn orange-brown with ribs red-brown, to 1.8 mm long, mostly less than 2: 1, erect, strongly sulcate with eight ribs, strangulate. Operculum short apiculate. Annulus well-defined, falling in fragments. Exothecial cells at capsule mouth strongly reddened, to 15 µm broad, isodiametric to transversely elongate with rounded lumens in up to 8 rows. Exothecial cells at middle of urn quadrate to rectangular, 1.5–2.5: 1, to 35 µm broad, thick-walled on ridges of capsule with lumen:wall ratio about 1: 1, thinner walled and somewhat more elongate in valleys of the sulcate capsule. Stomata present in proximal 1/2 of capsule wall, cryptoporous and almost completely obscured by subsidiary cells. Exostome teeth erect to weakly reflexed, usually 16 even in the newly deoperculate capsule, hyaline to pale brown, to 350 µm long, papillose-striate to almost smooth. Endostome segments 8, mostly shorter than the exostome and often wanting, smooth to lightly papillose. Calyptra campanulate, almost without plications, rather densely beset with papillose hairs. Spores to 12 µm, rather coarsely papillose.