Orthotrichum pylaisii, Bryol. Univ. 1: 722. 1826. -- Orthotrichum arcticum Schimp., Musci Eur. Nov. Bryol. Eur. Suppl. fasc. 1/2: 5. 5. 1864. -- Orthotrichum pylaisii ssp. arcticum (Schimp.) Kindb., Eur. N. Am. Bryin. 2: 302. 1897. -- Orthotrichum blyttii ssp. arcticum (Schimp.) Mac., Cat. Can. Pl. 7: 229. 1902. -- Orthotrichum microblephare Schimp., Musci Eur. Nov. Bryol. Eur. Suppl. fasc. 1/2: 2. 3. 1864. -- Orthotrichum pylaisii ssp. microblephare (Schimp.) Kindb., Eur. N. Am. Bryin. 2: 302. 1897. -- Orthotrichum rhabdophorum Vent. in Roell, Bot. Centralbl. 44: 418. 1890. -- Orthotrichum idahense Card. & Ther., Bot. Gaz. 30: 19. 1900.

   Plants dark green to brownish-green, in spreading mats or cushions with main axes to 3 cm long. Leaves spreading to strongly spreading when moist but appressed when dry, ovate-lanceolate to lanceolate, broadest immediately above the base, with apices broadly acute to obtuse or apiculate, to 2.5 mm long, about 3: 1. Median laminal cells to 12 µm wide, arranged in regular rows, isodiametric with lumens rounded due to the strong corner thickenings. Papillae arranged over the lumens on each surface, 1–3, often bifid. Basal marginal cells to 12 µm wide, isodiametric to short rectangular, mostly pachydermous and smooth not very auriculate. Basal juxtacostal cells mostly smooth, rectangular, to 14 µm wide, 3–6: 1, pitted, reddish-brown or concolorous. Cells on adaxial surface of costa elongate and pitted in 1–2 rows. Margins entire or papillose crenate, recurved from base to near the apex. Costa ending within a few cells of apex, lying in a sharply defined keel. Costa cross-section terete throughout, homogeneous, mostly 4 cells thick with more than 10 cells along the abaxial perimeter. Median axillary hairs with one basal brown cell, not offset from leaf insertion, to 5 cells and 120 µm long with the laterally inserted ones much shorter than the lateral ones. Rhizoids very sparsely produced at base of plant, to 20 µm in diameter at insertion, smooth, brown to red-brown, sparingly branched. Stem cross-section rounded pentagonal, with no central strand, mostly pachydermous and brownish-walled throughout, with 1–3 outer layers smaller and somewhat thicker walled.

   Autoicous with perigonia in leaf axils near the perichaetia. Perichaetial bracts not differentiated from vegetative leaves. Capsule emergent on a yellow to yellow brown, smooth and erect seta to 3 mm in length. Urn pale-brown with ridges reddened, to 2 mm long, 1.5–2: 1, erect, strongly sulcate with eight well-defined ribs, lightly or not at all strangulate. Operculum conic-apiculate to short rostrate. Annulus well-defined, falling in fragments. Exothecial cells in cross-section single-layered. Exothecial cells at capsule mouth often strongly reddened, to 35 µm wide, transversely elongate with rounded lumens in up to 6 rows. Exothecial cells at middle of urn rather thick walled with lumen: wall ratio 4–6: 1, short rectangular, 2–3: 1, to 25 µm broad in the valleys but only 15 µm on the ridges of the sulcate capsule. Stomata phaneroporous, scattered on proximal 1/2 of urn. Exostome teeth reflexed when dry, seldom or never fused in pairs, pale to light yellow, to 200 µm long, lightly to strongly papillose. Endostome segments absent or reduced and of only 1–2 rows of cells. Calyptra campanulate, demsely covered with papillose hairs. Spores green, to 25 µm, rather coarsely papillose.

Vouchers: Alpine Co.; Red Lake Creek, Toiyabe National Forest, Norris 88197; Fresno Co.: Spanish Mountain Jeep Road, Sierra National Forest, Shevock & York 12429; Humboldt Co.: Grouse Mountain Road about 3 miles northeast of Horse Mountain Road, Six Rivers National Forest, Norris 45777; Modoc Co.: Big Sage Reservoir north of Alturas, Norris 68497; Siskiyou Co.: McCloud River about 5 miles east of McCloud, Norris & Hillyard 103897; Trinity Co.: below Packer's Peak, Norris 8982.

Literature: Harthill et al. 1979; McGrew 1976; Showers 1982. As Orthotrichum microblepharum Spjut 1971.

Illustration References: Vitt 1973.

Elevation by latitude plot for Orthotrichum pylaisii
   in California