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Didymodon rigidulus Hedwig [Pottiaceae]
map of distribution

Plants to 1 cm high, in dense cushions, green to brownish green, sometimes nearly black in older portions. Dry leaves mostly appressed and not very crispate. Moist leaves ascending, to 2.5 mm long, about 3: 1, not keeled. Leaves lanceolate, gradually contracted from the moderately well-defined ovate base which constitutes 1/3–1/5 of leaf length, ending in a narrowly subulate but blunt apex Median cells unistratose throughout or with bistratose streaks near the leaf apex, mostly with a few low and inconspicuous papillae but occasionally smooth, to 8 µm broad, in straight rows, lumen/wall ratio 2–4: 1, quadrate with rounded lumens due to strong corner thickenings. Cells of margin somewhat smaller and thicker walled. Basal cells arranged in regular rows, moderately thick-walled with the lumen/wall ratio about 2–4: 1, short rectangular mostly in a large basal group, to 10 µm broad, 2–4: 1, with straight and not pitted lateral walls. Ad- and ab-axial surface of costa clothed with isodiametric cells like those of the lamina. Costa at base 8–10 cells wide and occupying about 1/8 of leaf, not tapering, percurrent in a blunt apex. Costa cross-section semicircular bulging dorsally, with strong dorsal and ventral stereids, a single layer of guide cells, and well-differentiated epidermal cells on both surfaces. Margin entire, bistratose distally, recurved at least near leaf middle. Gemmae occasional in upper leaf axils, multicellular, green to brown, nearly spherical, to 50 µm in diameter. Axillary hairs to 100 µm, 4-celled with one basal brown cell. Stem round to rounded pentagonal in cross-section, with central strand, and with thin-walled inner cortical cells grading to 1–3 layers of thicker walled, smaller outer cortical cells. Rhizoids smooth, pale brown, sparingly branched, mostly restricted to base of plant, to 10 µm wide at insertion.
   Dioicous. Perichaetial leaves not significantly different from vegetative leaves. Setae to 15 mm, yellow brown to brown or reddish-brown, straight, smooth. Capsule erect and symmetrical with the urn cylindrical, to 2 mm long, about 3–4: 1. Operculum conic to short rostrate, to 3/4 of urn length. Exothecial cells with walls to 5 µm thick, rectangular, not in regular rows, to 25 µm wide, 2–4: 1, isodiametric, smaller and thicker-walled near mouth. Annulus poorly demarcated, persistent or falling in fragments. Peristome reddish-brown, to 1500 µm long, divided to base, without basal membrane, with the segments papillose-spiculose throughout, straight to strongly spiral. Spores spherical, about 10 µm, nearly smooth.

This plant has traditionally been considered to have a rather short and abortive peristome, but many examples from California have a peristome as long and well-developed as that of D. vinealis. This is one of the reasons for my acceptance of the views of Zander (1978) and of Saito (1975) who supplied a circumscription of the genera Barbula and Didymodon quite different from the traditional peristome-based distinctions.

Mail a correction to Paul Wilson ·
LiteratureBourell 1981; Flowers 1973; Kellman 2003; Lawton 1971; Shevock and Toren 2001; Sigal 1975; Yurky 1990, 1995. As Barbula acuta Koch 1950a; Lawton 1971. As Barbula rigidula Kingman 1912; Harthill et al. 1979; Koch 1950a; Long 1978; Watson 1880. As Didymodon mexicanus var. subulatus Harthill et al. 1979; McCleary 1972. As Didymodon rigidulus var. icmadophilus Zander 1981b, 1993. As Trichostomum rigidulum Lesquereux 1868; Lesquereux and James 1884; Moxley 1928.
IllustrationsCrum and Anderson 1981; Flowers 1973; Ignatov and Ignatova 2003; Ireland 1982; Lawton 1971; Sharp et al. 1994; Smith 1978; Zander 1993.
BioregionsCW, NW, SN, SW.
VouchersAlameda Co: Brushy Peak northeast of Livermore, Norris 87188; Fresno Co.: divide above Boyden Cave, Monarch Wilderness, Sequoia National Forest, Shevock & York 12330 and Warthan Creek about 7 miles west southwest of Coalinga, San Joaquin Valley, Norris 55135; Lake Co.: Highway 53 about 1 mile south of Highway 20, Norris 47687; Marin Co.: Bootjack Trail, Mt. Tamalpais State Park, Yurky 860 (SFSU); San Benito Co.: Clear Creek, San Benito Mountain, BLM Clear Creek Recreation Area, Shevock, Norris, & Hamon 20303 (determined by Zander); San Bernardino Co.: Highway 40 about 15 miles east of Barstow, Mojave Desert, Norris 68082; San Diego Co.: Matagual Creek, Volcan Mountains, Stark 611 (BUF); San Francisco Co.: Golden Gate Park, Shevock 19515; Siskiyou Co.: Elk Creek at Malone Creek south of Happy Camp, Norris 52250.
   

Elevation by latitude plot for Didymodon rigidulus
   in California

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