Musci Rec. 2(2): 23. 1801. -- Dorcadion obtusifolium (Brid.) Lindb., Musci Scand. 29. 1879. -- Stroemia obtusifolia (Brid.) I. Hag., Vid. Selsk. Skrift. 1907(3): 94. 1908. -- Nyholmiella obtusifolium (Brid.) Holmen & Warncke, Saert. Bot. Tids. 65: 179. 1969.
Orthotrichum inflexum C. Muell., Syn. 1: 690. 1849.
Plants to 2 cm high, closely arranged and erect in dark green to yellow-brown mats or tufts, often reddened toward the apices. Leaves erect-spreading when moist but loosely appressed when dry, ovate-lanceolate and broadest near the base, with bluntly rounded apices, to 2 mm long, about 3.5–4: 1. Median laminal cells mostly quadrate to somewhat elongate with the lumens irregular due to the strongly bulging trigones, to 12 µm wide, with 1–2 papillae on each surface. Basal marginal cells to 15 µm wide, quadrate and isodiametric, pellucid and smooth, often with hour-glass-shaped end walls. Basal juxtacostal cells smooth, elongate with oblique end-walls, to 4: 1, with lateral walls thick nd only moderately pitted. Cells on adaxial surface of costa elongate and pitted in 1–2 rows; those on abaxial costa isodiametric and similar to laminar cells. Margins entire to papillose-crenate, plane throughout or somewhat ascending near mid-leaf. Costa yellow, obscure distally, ending about 10–15 cells of apex, with leaf keeled along costa only above leaf middle. Costa cross-section essentially homogeneous, only 2 cells thick, and composed of 2 cells adaxially and about 3–5 cells abaxially. Axillary hairs to 6 cells long with the centrally inserted ones markedly longer than the lateral ones, to 200 µm long, with one basal brown cell, not offset from leaf insertion. Rhizoids to 15 µm in diameter at insertion, abundant except on youngest portions of stem, smooth, red-brown with pellucid lumens, extensively monopodially branched with the ultimate forks dichotomous and curved. Stem cross-section rounded pentagonal, without a central strand, with 2–4 layers of large and leptodermous, hyaline inner corticals and with 1–2 layers of strongly pachydermous, red brown outer cortical cells. Gemmae usually abundant, inserted primarily on adaxial surfaces of leaf lamina, uniseriate or with a few biseriate areas, to 45 µm wide, composed of 4–8 mostly red-brown and isodiametric cells.
Dioicous with male plants somewhat smaller than females. Perichaetia terminal with bracts smaller than vegetative leaves. Capsule immersed to somewhat emergent on a yellow to yellow brown, smooth and erect seta to 1 mm in length. Urn brown to dark brown, to 1.5 mm long, 2–3: 1, erect, strongly sulcate with eight well defined ribs which extend onto the long and rather well-defined neck, lightly strangulate. Operculum conic-apiculate. Annulus well-defined, revoluble. Exothecial cells at capsule mouth strongly reddened, to 15 µm wide, quadrate to transversely elongate with rounded lumens in up to 8 rows. Exothecial cells at middle of urn arranged in very regular rows, evenly rather thin-walled with lumen: wall ratio 6–10: 1, short rectangular, 1.5–4: 1, to 30 µm broad, only slightly thicker-walled on the ridges and thus rather poorly differentiated from the cells in the valleys of the strongly sulcate capsule. Stomata phaneroporous, primarily located near middle of the urn. Exostome teeth 8, reflexed when dry, pale brown, to 150 µm long, finely and densely papillose proximally, but often obliquely papillose striate distally. Endostome segments 8, about as long as the exostome, lightly or not at all papillose, comprised of two parallel rows of cells. Calyptra campanulate, essentially without plications or hairs. Spores green, to 25 µm, coarsely papillose.