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Bot. Centralbl. 44: 418. 1890. -- Orthotrichum microblephare var. praemorsum (Vent.) Grout, N. Am. Flora 15A: 10. 1946.
    Orthotrichum idahense Card. & Ther., Bot. Gaz. 30: 19. 1900.

Bot. Centralbl. 44: 418. 1890. -- Orthotrichum affine ssp. praemorsum (Vent.) Kindb., Eur. N. Am. Bryin. 2: 303. 1897. -- Orthotrichum microblephare var. praemorsum (Vent.) Grout, N. Am. Flora 15A: 10. 1946. -- Orthotrichum arcticum var. praemorsum (Vent.) Wijk & Marg., Taxon 10: 25. 1961.

Plants mostly rather closely branched with the branch tips curled when dry, to 1.5 cm high, erect to spreading in dark green to yellow-brown mats or tufts. Leaves erect spreading when moist but appressed when dry, lanceolate and broadest near the base, with acute apices, to 4 mm long, about 5: 1. Median laminal cells in very regular rows, isodiametric to slightly elongate with rounded lumens, thick walled with strong corner thickening, to 12 µm wide, with 1–2, usually bifid papillae on each surface. Basal marginal cells to 20 µm wide, nearly isodiametric, pellucid and smooth. Basal juxtacostal cells mostly smooth, rectangular, to 6: 1, strongly pitted, mostly reddish-brown. Cells on adaxial surface of costa elongate and pitted in 1–2 rows. Margins markedly papillose crenate, recurved from base to near the apex with the recurvature mostly describing more than a single complete spiral. Costa mostly strongly reddened, ending within about ten cells of apex, lying in a sharply defined abaxial keel. Costa cross-section essentially homogeneous, mostly 3 cells thick, and 6–8 cells wide along the abaxial perimeter. Axillary hairs only 2–3 cells long with the centrally inserted ones shorter than the lateral ones, to 75 µm long, with one basal brown cell, not offset from leaf insertion. Rhizoids to 25 µm in diameter at insertion, nearly restricted to base of plant, smooth, red-brown, monopodial and sparingly branched. Stem cross-section without a central strand, with somewhat pachydermous and hyaline inner corticals and with 1–2 layers of strongly pachydermous, red brown outer cortical cells.
    Autoicous with perigonia in leaf axils near the perichaetia. Perichaetia terminal with bracts smaller than vegetative leaves. Capsule immersed to somewhat emergent on a yellow to yellow brown, smooth and erect seta which seldom exceeds 1.5 mm in length. Urn pale yellowish, to 1.5 mm long, 1.5–2: 1, erect, wrinkled or lightly sulcate above but with eight well defined ribs on neck, lightly or not at all strangulate. Operculum conic-apiculate. Annulus well-defined, revoluble. Exothecial cells in cross-section. Exothecial cells at capsule mouth not strongly reddened, to 25 µm wide, transversely elongate with rounded lumens in up to 4 rows. Exothecial cells at middle of urn rather thick walled with lumen: wall ratio 4–6: 1, short rectangular, 2–4: 1, to 20 µm broad, mostly rather poorly differentiated between ridges and valleys of the only lightly sulcate capsule. Stomata phaneroporous, scarse and restricted to the extreme base of the urn. Exostome teeth reflexed when dry, initially fused in pairs but later separating, pale to light yellow, to 300 µm long, finely and densely papillose. Endostome segments mostly absent, occasionally 8 and short, smooth, arising from only one row of cells. Calyptra campanulate and fringed, heavily covered with papillose hairs. Spores green, to 22 µm, rather coarsely papillose.

Elevation by latitude plot for Orthotrichum praemorsum
   in California

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