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|Didymodon australasiae (W. J. Hooker & Greville) Zander [Pottiaceae]|
Mail a correction to Paul Wilson
Tortula australasiae Hooker & Greville, Edinburgh J. Sci. 1:301. 1824.
Didymodon diaphanobasis Cardot, Rev. Bryol. 37: 125. 1910.
Husnotiella torquescens (Cardot) Bartram, xxxxxxxxxxx
Trichostomopsis australasiae (Hooker & Greville) Robinson,xxxxxxxxxxx
Trichostomopsis brevifolia Bartram, Bryol. 34: 61. 1931.
Trichostomopsis diaphanobasis (Cardot) Grout, Moss Fl. N.Amer. 1: 228. 1939.
Trichostomopsis fayae Grout, Moss Fl. N.Amer. 1: 228. 1939.
Plant erect, dark green to almost black. Stems to 1 cm tall, spreading to almost squarrose when moist, erect-spreading when dry, not at all keeled. Leaves ovate to ovate-lanceolate, leaves to 1.5 mm long, somewhat appressed when dry. Leaves not keeled, only narrowly channeled along costa in distal region; broadly concave in at least the proximal ½, margins recurved in mid-leaf but with that recurvature suppressed by the bistratosity of the marginal cells. The costa is percurrent or nearly so, with elongate cells in 4–6 rows on adaxial face, ending in a blunt leaf apex, smooth, markedly tapering distally. Costa cross-section elliptical, about twice as broad as thick at mid-leaf, with differentiated abaxial and adaxial epidermises, with a group of 5–8 guide cells and with mostly a single abaxial stereid band. Median laminal cells isodiametric, to 12 m in diameter, rather thin-walled with small corner thickenings and with angular lumens, nearly smooth but with a few low papillae over the lumen, especially in distal, marginal portion of leaf. Basal laminal cells only gradually differentiated from median cells but consistently longer and broader, and with some of the pericostal basal cells inflated, 1–2.5:1, mostly smooth. Stem round in cross-section, with one layer of pale-brown and rather thick-walled cortical cells surrounding a hyaline and thin-walled central area with an inconspicuous central strand. Rhizoids scarce, to 6 mu at insertion. Axillary hairs 6–8 cells in length with the 2 basal brown cells elongate [3:1] with distal cells hyaline and thin-walled. Gemmae inconspicuous as multicellular, nearly spherical structures produced on short rhizoid inserted near stem base.
Dioicous with perichaetial leaves similar to vegetative leaves; costate and entire, with cells all smooth and thick-walled. Seta yellow but reddened with age, about 12 mm long. Calyptra cucullate, smooth and glabrous covering only part of the erect and stegocarpous capsule that is to 2 mm long, cylindric and symmetric. Exothecial cells nearly isodiametric, elliptic to hexagonal, thin-walled. Peristome teeth 16, divided nearly to base and terminating in filamentose, densely papillose threads seldom much twisted. Spores brown and spherical, about 15 µm in diameter, and finely papillose.
Didymodon australasiae occupies some of the most xeric geographic sites for the genus in California. I here make a distinction. I make here a distinction between xeric geographic sites such as deserts as opposed to xeric microsites that offer conditions of rapid drying, often in full sun. Didymodon australasiae has a complicated taxonomic history. This history is the result of an unusual combination of somewhat concave leaves, somewhat enlarged basal cells and several cells thickness of much of the leaf lamina. When Didymodon is encountered in the field, diagnosis as D. australasiae can be tentatively made by the nearly black coloration of entire margined leaves leaves with broad proximal concavities. Many populations of D. australasiae are in parks and other areas with heavy human use. In such areas, one will see plants trampled upon and these may appear to be one of the members of the genus often considered to have caducous leaf portions. Be careful not to ascribe this caducous condition to badly damaged plants.
|Literature||Shevock and Toren 2001. As Trichostomopsis brevifolia Bartram 1931; Harthill et al. 1979; Koch 1950a, 1951e; McCleary 1972; Steere 1954. As Trichostomopsis diaphanobasis Harthill et al. 1979. As Trichostomopsis faye Harthill et al. 1979; Koch 1950a; McCleary 1972; Steere 1954. As Trichostomopsis australasiae Lawton 1971.|
|Illustrations||Malcolm et al. 2009 p. 122; Allen 2002; Bartram 1931; Lawton 1971; Sharp et al. 1994.|
|Bioregions||CW, DMoj, DSon, SW.|
|Vouchers||Inyo Co.: Titus Canyon, Death Valley National Park, Norris 10206f; Kern Co.: Sand Canyon Road just north of Highway 58, Shevock 13237; Lake Co.: Chalk Mountain north of Cache Creek, Toren & Dearing 7310 (CAS); Los Angeles Co.: San Fernando Valley, MacFadden 21719 (MO); Riverside Co.: Snakeye Springs, Indian Cove, Joshua Tree National Park, Norris 57992; San Diego Co.: Box Canyon, Anza Borrego State Park, Colorado Desert, Norris 50630; San Francisco Co.: Golden Gate Park, Shevock 18896 (determined by Zander); San Luis Obispo Co.: about 1 mile west of Poso Grade, Norris 55215; Tuolumne Co.: along Highway 120 about 5 miles below Jamestown, Ikenberry 394 (MO) [determined by Grout].|