Cat. Can. Pl. 6: 202. 1892. -- Stereodon obtusifolius Mitt. J. Linn. Soc. Bot. 8: 42. 1864. -- Rhynchostegium obtusifolium (Mitt.) Jaeg., Ber. Sc. Gall. Naturw. Ges. 1876–1877: 377. 1878.
Plants in dense mats or floating streamers, sordid green to dark green. Stems to 15 cm long, prostrate, irregularly and sparingly branched, markedly julaceous. Leaves of stems and branches similar, to 1.8 mm, 1.5–2.0: 1, symmetric, oblong-ovate to elliptic, widest near middle, consistently blunt and obtuse or shortly apiculate at apex, concave, densely imbricated, somewhat wrinkled on drying. Margins mostly minutely recurved near insertion but sometimes nearly plane, neither decurrent nor cordate at base, nearly entire throughout or with slight serrulations distally. Median cells smooth, to 6 µm wide, linear-vermiculate, 10–20: 1, rather thin-walled. Alar cells undifferentiated or few and quadrate to short rectangular, thin-walled, only gradually differentiated from adjacent laminal cells. Basal cells well-demarcated in 1–3 rows, rectangular. 2–3: 1, thin-walled and translucent. Differentiated basal cells cloaking base of costa. One or a group of apical cells rhomboidal, 1–3: 1. Costa extending about 3/4–7/8, usually ending in one or several abaxial spines. Pseudoparaphyllia lanceolate, sharply dentate and acuminate, to 100 µm long. Axillary hairs 4-celled, to 75 µm without basal brown cells or with two very poorly differentiated ones, not offset from leaf insertion. Rhizoids red-brown, sparingly branched, to 15 µm at insertion, smooth, in scattered but dense fascicles on ventral surface of stem, especially near branch insertion.
Dioicous with male plants similar to females. Perichaetia on stoloniferous axis or on bases of branch axes, to 2.5 mm long. Perichaetial bracts ecostate, abruptly acuminate with divergent acumens from an ovate-lanceolate base; cells to 25: 1, with straight lateral walls. Seta to 1.5 cm long, red-brown, smooth below but lightly papillose and geniculate at apex. Capsule brown but dark at base, strongly strangulate. Urn arcuate, to 2.5 mm, 3–4: 1. Exothecial cells at middle of urn in more or less regular rows, to 25 µm wide, 2–3: 1, with thin but collenchymatous red-brown walls. Exothecial cells near mouth of capsule shorter and thicker walled than median exothecial cells, not in a well-demarcated band. Stomata numerous, phaneroporous, restricted to base of capsule. Operculum conic to short-rostrate, about 1/2 as long as urn. Exostome to 500 µm long, horizontally striate below, papillose above, red-brown, strongly trabeculate ventrally. Endostome segments low papillose, open on keel, about as long as exostome with basal membrane about as high as the segments. Cilia 2–3, appendiculate. Spores smooth to inconspicuously papillose, 10–14 µm.
|Literature||Bradshaw 1926; Harpel 1980a; Harthill et al. 1979; Holmberg 1969; Howe 1896; Jamieson 1969; Kellman 2003; Kingman 1912; Koch 1950a, 1951e, 1958; Koch and Ikenberry 1954; Lawton 1971; Long 1978; Mishler 1978; Shevock and Toren 2001; Showers 1982; Spjut 1971; Toren 1977; Yurky 1995.|
|Illustrations||Malcolm et al. 2009 p. 274; Flowers 1973; Lawton 1971.|
|Bioregions||CaR, CW, MP, NW, SN, SNE, SW.|
|Vouchers||Fresno Co.: Grizzly Falls along Highway 180, South Fork Kings River, Sequoia National Forest, Shevock 12433; Lake Co.: Upper Nye Camp just north of Snow Mountain Wilderness, Mendocino National Forest, Shevock, Bourell, & Toren 15833; Modoc Co.: Crowder Flat Road about 2 miles south of Oregon border, Norris 79145; Santa Barbara Co.: about 1 mile south of Bates Canyon Campground, Norris 55376; Riverside Co.: Gardner Valley, San Bernardino National Forest, Harpel 1954 (pers. herb.) [confirmed by Schofield]; Shasta Co.: Fall Creek Road at Dekkas Rock above Shasta Lake, Shasta-Trinity National Forest, Norris 84833.|