Didymodon occidentalis, Phytologia 41: 26. 1978. -- Barbula rubiginosa Mitt., J. Linn. Soc. Bot. 8: 27. 1864. --Didymodon vinealis var. rubiginosus (Mitt.). Zander, Cryptogamie 2: 417. 1981.

   Plants to 2 cm high, in dense tufts or cushions, dark green to brownish green, sometimes reddish in exposed sites. Dry leaves mostly appressed and not very crispate. Moist leaves spreading, to 2.5 mm long, about 3–4: 1, strongly grooved along distal portion of the costa. Leaves ovate lanceolate, gradually contracted from the moderately well-defined ovate base to the narrowly acute apex. Median cells unistratose throughout, mostly with a few low and inconspicuous papillae and only occasionally smooth, to 12 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. Differentiated elongate basal cells absent or occasionally present near costa at extreme leaf base, arranged in regular rows, moderately thick-walled with the lumen/wall ratio about 2–4: 1, to 12 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 about 8–10 cells wide and occupying about 1/6 of leaf, not tapering, percurrent in an acute apex. Costa cross-section semicircular bulging dorsally, with a single layer of guide cells and with a strong dorsal stereid band but with the ventral area composed primarily of substereidal cells, with well differentiated epidermal cells on both surfaces. Margin not or very shortly decurrent, entire, unistratose or with a few bistratose patches, recurved at base with recurvature usually extending above leaf middle. Gemmae absent. Axillary hairs to 100 µm, 4–5 celled with one basal brown cell. Stem 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 pale brown to brown, smooth, sparingly branched, mostly restricted to plant bases, to 12 µm wide at base.

   Dioicous. Perichaetial leaves not significantly different from vegetative leaves. Seta to 12 mm, red brown, straight, smooth. Capsule erect and symmetrical with the urn cylindrical, to 2.5 mm long, about 3–4: 1. Operculum long conic rostrate, to 1/2 of urn length. Exothecial cells with walls to 5 µm thick, quadrate to short-rectangular, in regular rows, to 20 µm wide, 4–6: 1, gradually smaller and thicker-walled near mouth. Stomates few, restricted to base of urn. Annulus of 1–2 rows of vesicular cells, persistent or falling in fragments. Peristome absent or very poorly developed, yellow- to reddish-brown, to 50 µm long, without basal membrane, with the teeth undivided or perforate, papillose-spiculose throughout, straight. Spores spherical, to about 10 µm, nearly smooth.

Vouchers: Colusa Co.: Highway 20 at milepost 74, Norris 52515, 52522, & 52526; Contra Costa Co.: Mitchell Canyon, Mt. Diablo State Park, Norris 100606; Fresno Co.: Warthan Creek about 7 miles southwest of Coalinga, Norris 55124; Kern Co.: Round Mountain Road, 5.79 miles east of junction with Granite Road and 1.9 miles west of Eastmont Road, north of Oildale, Shevock 14841; San Luis Obispo Co.: near Black Mountain and Navajo Camp about 1.5 miles west of road junction, Norris 55244.

Literature: Whittemore and Sommers 1999. As Barbula rubiginosa Harthill et al. 1979; Lawton 1971; Lesquereux 1868; Lesquereux and James 1884; Spjut 1971; Toren 1977.

Illustration References: Lawton 1971.

Elevation by latitude plot for Didymodon occidentalis
   in California