Didymodon tophaceus, Elenco Muschi Torino 31. 1837. -- Barbula tophaceus Brid., Musci Rec. Suppl. 4: 84. 1819. -- Didymodon hendersonii Ren. & Card., Bot. Gaz. 15: 40. 1890.

   Plants to 2 cm high, in dense turfs or cushions, green to olivaceous or dark green. Dry leaves spreading and laterally twisted, appearing quite distantly inserted. Moist leaves spreading, to 2 mm long, about 3: 1, strongly keeled. Leaves ligulate to ligulate lanceolate, broadest somewhat below middle, without a well demarcated base. Median cells quite variable in size and shape, unistratose, mostly with one or two low and inconspicuous papillae but occasionally smooth, to 12 µm broad, in straight rows, lumen/wall ratio 2–4: 1, quadrate to polygonal or somewhat transversely elongate, with rounded to irregular lumens due to strong corner thickenings. Cells of margin little differentiated. Basal cells in a small and inconspicuous group especially near costa, arranged in regular rows, moderately thick-walled with the lumen/wall ratio about 2: 1, short rectangular, to 14 µm broad, 1.5–2.5: 1, with straight and not pitted lateral walls. Ad- and ab-axial surface of costa clothed with isodiametric to short rectangular cells not strongly differentiated from those of the lamina. Costa at base more than 8 cells wide and occupying about 1/6 of leaf, rather obviously tapering toward apex, percurrent or ending within a few cells of the broadly acute to bluntly rounded apex. Costa cross-section semicircular bulging abaxially, with a well-differentiated abaxial epidermis but with the adaxial epidermis inconspicuous, with a single layer of guide cells and a strong abaxial stereid band but with the abaxial band absent or reduced to substereids. Leaves broadly decurrent with decurrency 4 or more cells wide at its broadest point. Margin entire to crenulate, unistratose or with a few bistratose streaks, recurved to above leaf middle. Gemmae not present. Axillary hairs to 75 µm, 3–4 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 2–3 layers of thicker walled, smaller outer cortical cells, without hyaloderm.

   Dioicous. Perichaetial leaves sheathing the base of the seta but otherwise not significantly different from the vegetative leaves. Setae to 10 mm, reddish-brown, straight, smooth. Capsule erect and symmetrical with the urn oblong to short cylindrical, to 1 mm long, about 2–3: 1. Operculum conic-rostrate, to 3/4 of urn length. Exothecial cells with walls to 5 µm thick, short-rectangular, in regular rows, to 25 µm wide, 1–3: 1, gradually smaller and thicker-walled near mouth. Annulus of about 2 rows of vesiculose cells, deciduous in fragments. Peristome mostly absent to rudimentary, occasionally to 200 µm long, hyaline to pale yellow, bluntly ligulate, mostly not divided or somewhat perforate, without basal membrane, with the segments papillose-spiculose throughout, mostly not twisted. Spores spherical, about 12 µm, nearly smooth.

Vouchers: Fresno Co.: just below bridge crossing of Highway 180 at Boyden Cave, Sequoia National Forest, Shevock 12459; Inyo Co.: Cottonwood Canyon, Cottonwood Mountains, Death Valley National Park, Shevock, Kellman, York, & Knaus 20559; Napa Co.: near Lake Berryessa about 4 miles east of Pope Valley, Norris 48257; Nevada Co.: Washington Road about 2.5 miles from Highway 20, Tahoe National Forest, Shevock & Toren 20711; Riverside Co.: Bay Tree Springs, San Jacinto Mountains, San Bernardino National Forest, Harpel 1848 (pers. herb.); Santa Barbara Co.: La Jolla Vieja Canyon, Santa Rosa Island, Channel Islands National Park, Shevock & Rodriquez 20867; Santa Clara Co.: Alum Rock Park, San Jose, Schofield 12697 (UC); Siskiyou Co.: Sawyers Bar to Forks of the Salmon Road about 2 miles east of Forks of the Salmon, Norris 22760.

Literature: Crum and Anderson 1981; Harpel 1980a; Harthill et al. 1979; Holmberg 1969; Kellman 2003; Kingman 1912; Koch 1950a; Lawton 1971; Long 1978; McCleary 1972; Millspaugh and Nuttall 1923; Mishler 1978; Shevock and Toren 2001; Sigal 1975; Steere 1954; Toren 1977; Yurky 1990, 1995. As Desmatodon hendersonii Koch 1950a; McCleary 1972; Millspaugh and Nuttall 1923; Steere 1954; Steere et al. 1954. As Trichostomum tophaceum Lesquereux 1868; Lesquereux and James 1884; Sullivant 1856; Watson 1880.

Illustration References: Malcolm et al. 2009 p. 126; Crum and Anderson 1981; Flowers 1973; Ignatov and Ignatova 2003; Lawton 1971; Sharp et al. 1994; Smith 1978.

Elevation by latitude plot for Didymodon tophaceus
   in California