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Fabronia pusilla Raddi [Fabroniaceae]
map of distribution
photo by Coleman 250

Plants in very thin to dense prostrate mats, yellow-green to green, irregularly to regularly pinnately branched with branches and stems little different. Leafy axes similar wet or dry, to 1 cm long. Leaves to 0.75 mm, about 3: 1, ovate lanceolate and abruptly contracted to a linear acumen which is formed of a single elongate cell, symmetric, closely imbricate when dry. Margins plane, not decurrent, coarsely serrate to fimbriate above the middle. Median cells smooth, to 10 µm wide, long rhomboidal to linear, up to 5: 1, thin walled, not pitted. Alar cells quadrate in a poorly defined cluster which often extends to the costa, to 12 µm wide. Costa narrow but well demarcated, ending near leaf middle. Pseudoparaphyllia deltoid to orbicular, strongly overarching the bud. Axillary hairs 3-celled, to 80 µm with no basal brown cells, not offset from leaf insertion. Stem cross-section without a central strand and with little or no differentiation of any outer thick walled cells.
   Autoicous. Perichaetia in leaf axils, with the bracts serrate, about as long as the subtending leaves. Seta to 2.5 cm long, erect, pale yellow to yellow brown. Capsule light brown, erect, neither sulcate nor strangulate. Urn oblong, widest at the mouth, to 1 mm, about 2: 1. Exothecial cells at mid urn short rectangular with somewhat sinuose and thin lateral walls, 1.5–3: 1, in regular rows, to 22 µm broad. Stomata phaneroporous, restricted to neck. Annulus present, not revoluble. Operculum conic, much shorter than urn. Exostome to 300 µm long with the teeth fused in pairs, finely papillose throughout, light-brown. Endostome absent. Spores lightly papillose, to 15 µm.

This abundant plant throughout much of California is absent from eastern North America but it reappears in Mediterranean climatic zones of Europe. It is regularly to be expected on the undersurfaces of large horizontal limbs of oaks in the Central Valley. It also may be found in small recesses in rather dry rock outcrops, and it forms especially luxuriant clones on limestone at mid elevations in the central to southern regions of the western Sierran foothills. It appears to be lacking at high elevations. Recognition characters for the genus are listed above, and the key should be consulted for species recognition.

Mail a correction to Paul Wilson ·
LiteratureBradshaw 1926; Harthill et al. 1979; Howe 1896; Kellman 2003; Koch 1950a, 1951e; Lawton 1971; Lesquereux 1868; Long 1978; Mishler 1978; Thomson and Ketchledge 1958; Toren 1977; Watson 1880.
IllustrationsMalcolm et al. 2009 p. 278; Lawton 1971; Sharp et al. 1994.
BioregionsCaR, CW, DMoj, NW, SN, SW.
VouchersContra Costa Co.: Mount Diablo State Park about 1.5 miles from entrance, Koch 1552 (UC); Inyo Co.: South Fork Hanaupah Canyon, east base of Telescope Peak, Death Valley National Park, Shevock & York 21354; Kern Co.: Horse Canyon, tributary of Cache Creek, 4 miles north of Highway 58, southern Piute Mountains, Shevock & Hare 14900; San Bernardino Co.: Waterman Canyon, San Bernardino National Forest, Harpel 2400 (pers. herb.); Tehama Co.: Antelope Creek Canyon near Microwave Station about 10 miles east of Red Bluff, Berti 415 (UC); Trinity Co.: Hall City Caves east of Wildwood, Shasta-Trinity National Forest, Norris 71664; Ventura Co.: Howard Creek Trail about 1 mile east of Highway 399, Norris 55483; Yuba Co.: Highway 20 near Timbuctoo, Norris 67488.

Elevation by latitude plot for Fabronia pusilla
   in California

Generated: Wed Sep 19 11:13:16 2018