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Brachythecium rivulare Bruch & W. P. Schimper [Brachytheciaceae]
map of distribution

Plants in very soft, loose mats, pale green to yellow-green or (in exposed sites) with a brownish cast, irregularly and sparingly branched or rather closely branched with the branches ascending to erect. Primary stems to 15 cm long with leaves somewhat larger and proportionately broader than those on the branches. Branch leaves to 2.5 mm, 1.2–1.5: 1, symmetric and straight but somewhat twisted to the left when dry, concave and smooth to lightly wrinkled or weakly plicate, broadly ovate to deltoid-ovate, imbricate to patent. Leaf apices broadly acute to mostly obtuse, often rather abruptly defined by an apical contraction. Margins somewhat recurved at base or completely plane, decurrent by 4–6 cells, distally serrulate but mostly entire in proximal one-half. Median cells smooth, spinulose and thin-walled, to 8 µm wide, mostly 8–12: 1, not pitted. Basal juxtacostal cells quadrate or nearly so, to 18 µm wide. Alar group triangular, extending 2/3 of way to costa and extending 4–10 cells up leaf (including the decurrency). Alar cells to 30 µm wide, 3–5: 1, thin-walled and pellucid. Marginal cells of alar region narrowly rectangular, to 12 µm wide, to 8: 1. Costa extending 1/2 to 3/4, tapering to apex but seldom terminating in an apical spine. Juvenile leaves to 200 µm long, elliptic, about 2: 1, coarsely serrate across the rounded to truncate apex. Axillary hairs to 70 µm, 2–3 celled with a single basal brown cell. Rhizoids sparse, mostly unbranched and light-brown, smooth, to 12 µm in diameter, clustered on the expanded abaxial costa base. Stem cross-section with central strand, a stereome 2–3 cells thick, but without an hyaloderm.
    Dioicous with male plants typically somewhat smaller than the females. Perigonia sparingly produced on prostrate stem and large branches. Perichaetial leaves about 1 mm long, ecostate and not plicate, without alar differentiation but with the median cells quite strongly prorate, sheathing at base but reflexed distally. Seta coarsely papillose throughout, 10–20 mm long, erect or distally geniculate. Capsule dark brown to reddish brown, inclined to horizontal, not distorted or sulcate when dry. Urn to 4.5 mm, 4–5:1. Exothecial cells in regular rows but irregular in size and shape, to 25 µm wide, 1–3: 1, with lateral walls thick (lumen: wall ratio 2–3: 1) but transverse walls thinner, mostly oblique to long axis of capsule. Stomata few, restricted to neck, short and vertical pored. Operculum conic, about 1/4 as long as urn. Exostome teeth inserted at capsule mouth but somewhat fused basally, to 600 µm long, narrowly lanceolate with inconspicuous shoulders, about 6: 1, horizontally striate, yellowish, inflexed when dry. Endostome segments about as long as exostome with basal membrane comprising about 1/2 of total length. Spores smooth, 12–18 µm.

A straight line from costa insertion across the leaf will usually define the line between the alar group and the distal laminal cells.

European materials seem to have leaves more strict with the costa stronger and with the alar region less pronounced.

Mail a correction to Paul Wilson ·
LiteratureHolmberg 1969; Moxley 1928; Spjut 1971.
IllustrationsAbramov and Volkova 1998; Buck 1998; Flowers 1973; Ignatov 1998; Ignatov and Koponen 1996; Ireland 1982; Koponen et al. 1995; Lawton 1971; Robinson 1962; Smith 1978.
BioregionsCaR, MP, NW, SN, SNE.
VouchersHumboldt Co.: Forest Road 10N02 at head of Mill Creek, Norris 70585; Inyo Co.: Goodale Creek at BLM Goodale Campground, Shevock & Norris 16854; Modoc Co.: Cottonwood Flat Campground, Modoc National Forest, Norris 68523a; Mono Co.: Lundy Lakes Trail along Mill Creek below Lake Helen, Inyo National Forest, Norris 78869; Placer Co.: road to Bowman Lake about 2 miles from Highway 20, Tahoe National Forest, Norris 77005; Tulare Co.: Nobe Young Creek, Sequoia National Forest, Laeger 12 (CAS) and Oriole Lake, Sequoia National Park, Norris, Shevock, & Barahona 87554.
   

Elevation by latitude plot for Brachythecium rivulare
   in California

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