Amblystegium serpens

   Plants in loose and rather thin mats, pale to rich green, often with a russet cast. Stems to 5 cm long, prostrate to weakly ascending, irregularly branched. Stem leaves erect-spreading to spreading, to 1.2 mm, 2.5–3: 1, symmetric and lanceolate to narrowly ovate-lanceolate, not at all plicate, long acuminate with the acumens straight, little changed moist or dry. Branch leaves smaller than stem leaves, less spreading but not otherwise different. Leaf margins plane and entire or weakly serrulate in distal 1/3, not decurrent. Median cells smooth, to 8 µm wide, long rhomboidal, 3–5: 1, rather thin-walled, not pitted. Alar cells quadrate with walls not strongly thickened, only gradually differentiated from adjacent laminal cells. Apical cells gradually somewhat more elongate than median cells. Costa extending 1/3–2/3, not reaching the acumen, without an abaxial spine. Pseudoparaphyllia deltoid to lanceolate, strongly overarching the bud. Axillary hairs of 3 similar cells, to 60 µm with no basal brown cells, not offset from leaf insertion. Rhizoids red-brown, 12–14 µm, smooth, in scattered fascicles on ventral portion of prostrate stem.

   Autoicous with perigonia near perichaetia. Perichaetial bracts costate, abruptly acuminate from a ligulate-lanceolate base, cells uniformly long and straight to 10: 1. Seta yellow-to red-brown, smooth, to 2 cm long. Capsule brown to dark brown, inclined to horizontal, not strangulate. Urn to 1.5 mm, short cylindric to oblong, somewhat arcuate, 2.5–3.5: 1. Exothecial cells in regular vertical rows, to 20 µm wide, mostly 2: 1 but some to 4: 1, with moderately thick, red-brown walls and with stomata restricted to neck. Operculum conic to short-rostrate, about 1/4 as long as urn. Annulus differentiated, not revoluble. Exostome to 500 µm long, horizontally striate below, papillose above, yellow- to 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. Spores finely papillose, to 15 µm.

Vouchers: Los Angeles Co.: Devil's Punchbowl Canyon, San Gabriel Mountains, Angeles National Forest, Harpel 582 (pers. herb.); Monterey Co.: Arroyo Seco, Norris 48517; San Francisco Co.: Golden Gate Park, Koch 1635 (UC) and Norris & Shevock 97033; Tulare Co.: Cedar Creek, South Fork Kaweah River, Sequoia National Park, Showers 3273 (SFSU) and Kern Plateau off of Sirretta Pass Trail above Big Meadows, Sequoia National Forest, Shevock & Ng 17553.

Literature: Harpel 1980a; Harthill et al. 1979; Kellman 2003; Kingman 1912; Koch 1950a, 1951e, 1958; Lawton 1971; Long 1978; Shevock and Toren 2001; Showers 1982; Spjut 1971; Strid 1974; Toren 1977. As Hypnum serpens Lesquereux 1868; Sullivant 1856; Watson 1880.

Illustration References: Malcolm et al. 2009 p. 228; Buck 1998; Flowers 1973; Ireland 1982; Lawton 1971; Smith 1978.

Elevation by latitude plot for Amblystegium serpens
   in California