Plants in cushions, mats or pendent streamers, olive-green to whitish-green, often with a russet cast. Stems to 10 cm long, ascending to erect; or pendent to 50 cm long. Pinnately branched and julaceous with branches of pendent plants microphyllous and attenuate, sometimes with the entire plant composed of such branchlets. Leaves to 3.5 mm, 4–7:1, symmetric, sagittate- to ovate-lanceolate, acuminate, often with the apex twisted, loosely imbricate when dry and little changed when moist. Margins plane but sometimes ascending in the acumen, not decurrent, entire to serrulate below the middle, coarsely serrate above. Median cells mostly smooth but usually with some dorsal prorations in distal portion of leaf, 5–12 µm wide, 6–10:1, moderately thick-walled with lumen/wall ratio to 2:1, usually pitted. Alar cells quadrate and very thick-walled (lumen/wall ratio 0.5–1:1), with intensely green contents, abruptly differentiated from adjacent laminal cells, often in an excavate pocket. Apical cells rhomboidal, nearly isodiametric. Costa extending about 3/4, usually ending in an abaxial spine. Pseudoparaphyllia deltoid to orbicular, strongly overarching the bud. Axillary hairs 5-celled, to 120 µm with 2 basal brown cells, not offset from leaf insertion. Rhizoids red-brown, 10–12 µm, smooth, in scattered fascicles on ventral portion of prostrate stem.
Dioicous with male plants similar to females. Perigonia on main axis or on larger lateral branches. Perichaetia on main axis, to 2.5 mm. Perichaetial bracts ecostate, abruptly acuminate from a ligulate-lanceolate base, cells long vermicular, to 25:1. Seta to 2 cm long, exserted. Capsule brown, inclined to horizontal, not distorted or sulcate when dry. Urn to 2 mm, 2–3:1. Exothecial cells in regular vertical rows, to 25 µm wide, 1–2:1, with thick (lumen/wall ratio 4–6:1), red-brown walls, stomata restricted to neck. Operculum conic to short-rostrate, about 1/4 as long as urn. Exostome horizontally striate below, papillose above, yellow-brown. Endostome segments low papillose, open on keel, about as long as exostome with basal membrane about as high as the segments. Cilia 2, not appendiculate. Spores papillose, 15–20 µm.
| Literature | Ireland 1982. As Amblystegium compactum Cheney 1897; Flowers 1973; Koch 1950a; Koch and Ikenberry 1954; Lesquereux 1868; Steere 1954. As Rhynchostegiella compacta Harthill et al. 1979; Lawton 1971; Long 1978; McCleary 1972. |
| Illustrations | Malcolm et al. 2009 p. 230; Flowers 1973; Hedenäs 1989a, 1993a, 2003; Ireland 1982; Lawton 1971; Sharp et al. 1994. |
| Bioregions | DMoj, DSon, NW, SN, SNE, SW. |
| Vouchers | Inyo Co.: Pine Creek Trail less than 0.5 mile from end of Pine Creek Road, Inyo National Forest, Shevock, Halford, & Nelson 15308; Lake Co.: along road to Harlin Springs south of Boggs Mountain, Toren & Dearing 7281 (CAS); Mariposa Co.: Highway 49 above Hells Hollow near milepost 32, Shevock 18749; Siskiyou Co.: Shasta Springs, Howe 127 (UC); Tulare Co.: Coy Flat Road, 0.25 mile south of bridge crossing of Middle Fork Tule River below Camp Nelson, Sequoia National Forest, Norris, Shevock, & Barahona 87663 & 87679; Ventura Co.: road to summit of Mt. Pinos about 1 mile below Chula Vista Campground, Los Padres National Forest, Laeger 1718 (CAS). |
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