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Plagiothecium laetum Bruch & W. P. Schimper [Plagiotheciaceae]
map of distribution

Plants prostrate, scattered or in loose mats, glossy light green to yellow green, mostly rather sparingly branched. Leafy axes to 3 cm long, mostly tapering near the branch tips, strongly complanate with leaves imbricate, often strongly so, not at all undulate. Leaves to 1.5 mm, 3–4: 1, asymmetrically ovate to ovate-lanceolate, acute to acuminate at apex. Margins nearly entire but mostly with a few light serrulations near apex, plane or more often narrowly recurved. Decurrency distally 2–3 cells wide but only one cell wide over most of its length. Median cells smooth, to 8 µm wide, linear, up to 20: 1, thin walled, not pitted. Alar and basal cells only gradually demarcated, shorter than and somewhat more thick-walled than median cells. Costa short and double with the two branches unequal. Pseudoparaphyllia deltoid to orbicular, strongly overarching the bud. Cortical cells of stem broad in surface view thin-walled, rectangular, 3–8: 1; to 20 µm wide. Axillary hairs 5-celled, to 250 µm with a single basal brown cell, not offset from leaf insertion. Stem cross-section with an obscure central strand, with a markedly enlarged hyaloderm relative to the adjacent several layers of small and brownish somewhat pachydermous cells, and with inner cortical cells enlarged with thin and hyaline walls. Gemmae and propagules seemingly absent from California specimens.
   Autoicous. Perichaetia in axils of stolons, somewhat shorter than the subtending leaves. Seta to 3 cm long, erect or distally geniculate, light brown to yellow brown when mature. Capsule brown, inclined, somewhat arcuate, smooth to lightly sulcate, markedly strangulate at mouth. Urn to 3 mm, 2.5–3: 1. Exothecial cells at mid urn short rectangular, 1.5–3: 1, in regular rows, not collenchymatous, to 30 µm broad. Exothecial cells near mouth of capsule not strongly differentiated, mostly with walls somewhat thicker than those of median cells. Stomata phaneroporous, restricted to neck. Annulus present, not revoluble. Operculum short-rostrate, about 1/3 as long as urn. Exostome to 500 µm long, closely horizontally striate below, papillose above, light-brown. Endostome segments lightly papillose, narrowly or not at all perforate, about as long as exostome with basal membrane about 1/2 of total length. Cilia 2–3, nodose. Spores smooth, to 12 µm.

Mail a correction to Paul Wilson ·
LiteratureBourell 1981; Ireland 1982, 1986; Kellman 2003; Lawton 1971; McGrew 1976; Shevock and Toren 2001; Smith 1970; Spjut 1971.
IllustrationsIgnatov et al. 1996, Ireland 1982, 1986; Lawton 1971.
BioregionsCW, NW.
VouchersDel Norte Co.: Damnation Creek Trail, Del Norte Redwoods State Park, Norris 46226; Humboldt Co.: Emerald Creek at junction with Redwood Creek, Redwood National Park, Norris 45835; Lake Co.: Bucknell Creek north of Garrett Mountain, Mendocino National Forest, Toren & Dearing 7414 (CAS); Mendocino Co.: along County Road 409 about 1 mile east of Highway 1 south of Fort Bragg, Norris 11691; San Francisco Co.: Golden Gate Park, Shevock 18760; Santa Cruz Co.: south of Santa Cruz, Forest of Nisene Marks State Park, Norris 55624.
   

Elevation by latitude plot for Plagiothecium laetum
   in California

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