Didymodon revolutus, Bryologist 16: 25. 1922. -- Husnotiella revoluta Card., Rev. Bryol. 36: 71. 1909. -- Husnotiella palmeri Card., Rev. Bryol. 37: 121. 1910. -- Husnotiella revoluta var. palmeri Card., Smiths. Misc. Coll. 85(4): 7. 1931.

   Plants to 0.5 cm high, in rather loose turfs, green to brownish green. Dry leaves appressed, with inflexed apices, mostly rather distantly inserted. Moist leaves widely spreading, to 1.5 mm long, about 2: 1, strongly channeled along costa. Leaves ovate to elliptic ovate, broadest somewhat below middle, without a well demarcated base. Median cells unistratose, mostly with one rather high papilla but occasionally smooth, to 8 µm broad, in straight rows, lumen/wall ratio 2–3: 1, quadrate with rounded 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, thick-walled with the lumen/wall ratio about 2: 1, mostly quadrate to short rectangular, to 10 µm broad, 1–1.5: 1, with straight and not pitted lateral walls. Ad- and ab-axial surface of costa clothed with isodiametric to short rectangular cells not strongly demarcated from those of the lamina. Costa at base more than 8 cells wide and occupying about 1/4 of leaf, rather obviously tapering and spurred toward the apex, ending within a few cells of the obtuse to bluntly rounded, mostly cucullate apex. Costa cross-section semicircular bulging abaxially and somewhat bulging adaxially, 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. Margin only slightly decurrent, entire to crenulate, unistratose or with a few bistratose streaks, mostly strongly recurved to above leaf middle. Gemmae occasionally present, unicellular, spherical to elliptical, to 15 µm wide, closely clustered in axils of upper leaves. Axillary hairs to 200 µm, to 8 celled with one basal brown cell. Stem rounded pentagonal in cross-section, with central strand, and with thin-walled inner cortical cells grading to 2–3 poorly demarcated layers of somewhat thicker walled and smaller outer cortical cells, mostly with a poorly developed hyaloderm.

   Dioicous. Perichaetial leaves loosely sheathing the base of the seta, somewhat smaller than adjacent vegetative leaves. Setae to 7 mm, reddish- to yellow-brown, straight, smooth. Capsule erect and symmetrical with the urn oblong to short cylindrical, to 1.5 mm long, about 3: 1. Operculum conic-rostrate, to 3/4 of urn length. Exothecial cells with walls only moderately thickened, short-rectangular, in regular rows, to 20 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 100 µm long, pale yellow, bluntly ligulate, mostly not divided or somewhat perforate, without basal membrane, with the segments papillose-spiculose throughout, not twisted. Spores spherical, about 10 µm, nearly smooth.

Vouchers: Contra Costa Co.: Pine Canyon near Castle Rocks, Mt. Diablo State Park, Norris 100792; Lassen Co.: Highway 139 about 16 miles south of Adin, Norris 21462 & 21466; Modoc Co.: Alturas, North Fork Pit River, Richards & Drouet 1263 (UC); Placer Co.: American River Canyon at junction of Highway 49 and Foresthill Road, Whittemore 4339 (MO); San Luis Obispo Co.: Boy Scout Road about 1 mile east of Twin Bridges, Camp Roberts Military Reservation, Norris 100885; Sonoma Co.: Adobe Canyon, Koch 285 (UC) and near Kenwood, Koch s.n. (MO) [determined by Bartram]; Tulare Co.: Limestone Campground, Kern River Canyon, Sequoia National Forest, Norris, Shevock, & Barahona 87102; Tuolumne Co.: about 5 miles below Jamestown, Ikenberry 394 (CAS) [determined by Koch].

Literature: As Husnotiella revoluta Bartram 1926; Grout 1928-40; Harthill et al. 1979; Koch 1949a, 1950a; Koch and Ikenberry 1954.

Illustration References: Allen 2002; Crum and Anderson 1981; Sharp et al. 1994.

Elevation by latitude plot for Didymodon revolutus
   in California