Brachythecium asperrimum

   Plants in rather dense mats to wefts, green to yellowish green. Stems prostrate to ascending, to 15 cm long, irregularly to pinnately branched with branches mostly weakly ascending. Leaves loosely imbricate when dry but erect spreading when moist, not at all falcate secund, to 2 mm long, 2–3: 1, deltoid to broadly ovate-lanceolate, somewhat concave and plicate, with a moderately well-defined, often twisted acumen. Branch leaves smaller and narrower than the stem leaves. Margins plane, decurrent, serrulate below but serrate near apices. Median cells smooth, to 8 µm wide, linear, about 10: 1, rather thick-walled, not pitted. Cells enlarged, rectangular, to 15 µm wide, in 2–3 rows across the entire base. Apical cells elongated, not differentiated. Costa extending 2/3–3/4, usually with an abaxial spine on at least some of the branch leaves. Pseudoparaphyllia deltoid to orbicular, strongly overarching the bud. Axillary hairs of 3 similar cells, to 50 µm with no basal brown cells, not offset from leaf insertion. Rhizoids red-brown, 10–12 µm, smooth, scattered in fascicles on ventral portion of prostrate stem.

   Dioicous with male plants somewhat smaller than females. Perichaetial bracts to 1.8 µm, costate, abruptly acuminate from a ligulate-lanceolate base with the acumens loosely spreading; cells uniformly long and straight to 20: 1. Seta brown to red-brown, straight, papillose throughout, to 3 cm long. Capsule brown, inclined to horizontal, strangulate when dry. Urn to 2.5 mm, oblong and asymmetric, to 2: 1. Exothecial cells mostly not in regular vertical rows, to 20 µm wide, mostly 2: 1, with thick, red-brown walls and with stomata restricted to neck. Operculum bluntly conic, about 1/3 as long as urn. Annulus differentiated, not revoluble. Exostome to 400 µm long, horizontally striate below, papillose above, red-brown. Endostome segments low papillose, open on keel, about as long as exostome with basal membrane about equal in length to the segments. Cilia 2–3, nodose to appendiculate. Spores finely papillose, to 15 µm.

Vouchers: Fresno Co.: Cedar Grove at Cedar Creek, Kings Canyon National Park, Shevock 13764; Humboldt Co.: Highway 299 east of Arcata, Norris 55082; San Francisco Co.: Chain of Lakes, Golden Gate Park, San Francisco, Shevock 19163; Santa Cruz Co.: Big Basin State Park, Schofield 6357 (CAN) [determined by Crum]; Tulare Co.: north base of Slate Mountain, Sequoia National Forest, Shevock 15661.

Literature: Flowers 1973; Holmberg 1969; Jamieson 1969; Kellman 2003; Koch 1950a; Koch and Ikenberry 1954; Lawton 1971; Shevock and Toren 2001; Spjut 1971; Toren 1977. As Brachythecium washingtonianum Crum 1957; Koch 1950a, 1958; Koch and Ikenberry 1954. As Hypnum asperrimum Watson 1880. As Hypnum vallium Lesquereux 1868.

Illustration References: Flowers 1973; Lawton 1971; Robinson 1962.

Elevation by latitude plot for Brachythecium asperrimum
   in California