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Orthotrichum pumilum Sw. [Orthotrichaceae]
map of distribution

Orthotrichum brachytrichum Schimp. ex. Lesq. & James, Proc. Am. Ac. Arts Sc. 14: 140. 1879.
   Orthotrichum fallax var. truncatulum Aust., Bull. Torr. Bot. Club 6: 344. 1879.
   Orthotrichum pumilum var. americanum Vent. in Husn., Musc. Gall. 180. 1887.

Plants erect in small green to rather dark green tufts, to 5 mm high. Leaves spreading when moist but, when dry, loosely erect with apices not incurved. Leaves to 2.5 mm long, about 3: 1, ovate-lanceolate to lanceolate with obtuse to rounded but minutely apiculate apices. Median laminal cells isodiametric with rounded lumens, thick walled with strong corner thickening, to 18 µm wide, smooth or with 1–2 very low papillae on both surfaces. Basal juxtacostal cells pellucid and rectangular, 1.5–2.5:1, to 24 µm wide with lateral walls straight but somewhat unevenly thickened. Basal juxtamarginal cells isodiametric and similar to median laminal cells. Margins recurved from base to near the apex, entire or 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 only 2 cells thick and up to 4 cells wide. Axillary hairs mostly rather uniform in size, to 5 cells and 100 µm long, with one basal brown cell, not offset from leaf insertion. Rhizoids abundant near base of plant but also present even on distal portions of plant, smooth, pale-brown to red-brown, to 30 µm in diameter at base, sparingly branched. Stem cross-section without a central strand, with hyaline inner corticals and with 1–2 layers of somewhat thicker-walled, red brown outer cortical cells. Gemmae scattered on adaxial leaf surface, to 25 µm in diameter, composed of 3–4 essentially isodiametric, green cells
    Autoicous with perigonia in leaf axils near the perichaetia or on the apices of separate short branches. Perichaetial bracts similar to the vegetative leaves. Capsule immersed to slightly emergent on a yellow to yellow brown, smooth and erect seta of about 0.5 mm in length. Urn orange-brown when fresh, to 2 mm long, 2–3: 1, erect, strongly sulcate with eight ribs, strongly strangulate. Operculum short rostrate. Annulus well-defined, falling in fragments. Exothecial cells at capsule mouth strongly reddened, to 20 µm broad, isodiametric to transversely elongate with rounded lumens in up to 4 rows. Exothecial cells at middle of urn quadrate to rectangular, 1.5–3: 1, to 30 µm broad, thick walled on ridges of capsule with lumen:wall ratio about 1: 1, thinner walled and more elongate in valleys of the sulcate capsule. Stomata present near middle of capsule wall, cryptoporous, only partially obscured by subsidiary cells. Exostome teeth strongly reflexed against capsule wall when dry, fused in pairs and appearing to be only 8 in number, light brown, to 300 µm long, finely and densely papillose. Endostome segments 8, mostly shorter than the exostome and often wanting, lightly papillose. Calyptra campanulate, mostly naked of hairs. Spores green, to 18 µm, rather coarsely papillose.

Mail a correction to Paul Wilson ·
LiteratureHarpel 1980a, 1980b.
IllustrationsIgnatov and Ignatova 2003; Ignatov and Lewinsky-Haapasaari 1994; Lawton 1971; Vitt 1973.
NotesName will change to Orthotrichum schimperi Hammar.
BioregionsCaR, NW, SN, SW.
VouchersLake Co.: Highway 53 about 1 mile south of Highway 20, Norris 47673 and Upper Lake Ranger Station, Mendocino National Forest, Toren 7436a (CAS) [determined by Vitt]; Orange Co.: Harding Canyon about 0.5 mile north of Mojeska Canyon and Tucker Bird Sanctuary, Cleveland National Forest, Shevock 4003; San Bernardino Co.: Waterman Canyon, San Bernardino National Forest, Harpel 2398 (pers. herb.); Santa Barbara Co.: about 1 mile south of Bates Canyon Campground, Norris 55381; Shasta Co.: County Road A16 about 14 miles east of Platina, Norris 23764; Tulare Co.: Highway 190 at Moorehouse Springs Creek, Sequoia National Forest, Norris 50924 and between Posey to White River, Kellman 1453 (CAS).
   

Elevation by latitude plot for Orthotrichum pumilum
   in California

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