Plants to 1.5 cm high, in hoary green to gray-green cushions, opaque-green to nearly black below. Leaves loosely imbricate when dry, loosely erect-spreading when moist, somewhat concave but not at all keeled, to 3 mm long with the awn constituting nearly 1/2 of that length, ovate-lanceolate from a loosely sheathing somewhat expanded base, 2.5–3.5: 1. Median leaf cells in regular longitudinal rows, unistratose in the expanded base but uniformly bistratose in the limb, smooth, to 7 µm wide, isodiametric with lumens irregular but without corner thickenings. Marginal cells not differentiated. Basal juxtacostal cells elliptical, to 3: 1, to 15 µm wide, with irregularly thickened lateral walls. Basal marginal cells transversely elongate, 0.5–0.7: 1, to 15 µm wide. Costa flared at the base and filling 1/3–1/4 of immediate leaf base, narrowed and obscure above, percurrent in the somewhat acuminate awn. Costa cross-section at leaf middle broad and flattened, less than 1.5 times as thick as the adjacent leaf, with a weak abaxial band of stereids or substereids and with a single layer of larger cells on the adaxial face. Margin of leaf limb plane to incurved, entire below. Awn strongly decurrent with its margin somewht serrulate, and with its surface spinose-prorate. Axillary hairs to 100 µm long, with 6–8 nearly isodiametric and thick- walled cells, without a basal brown cell. Rhizoids red brown, to 15 µm wide at base, smooth. Stem cross-section rounded-triangular with a large and well-defined central strand, and with leptodermous, hyaline and large inner cortical cells, and with the 1–2 cell-thick outer stereome composed of much smaller, thick-walled cells strongly pigment with yellow to yellow-brown.
Dioicous with male and female plants similar. Perichaetial leaves loosely sheathing base of seta, somewhat larger and with a relatively longer, less decurrent awn than the adjacent vegetative leaves. Seta to 2.5 mm long, yellow to pale brown, straight and smooth. Urn erect, symmetrical, smooth to lightly wrinkled when dry, to 1.2 mm long, 1.5–2: 1, not strumose. Operculum short rostrate, about 1/3 as long as urn. Annulus formed of 2–3 rows of relatively more thin-walled cells. Calyptra mitrate, covering about 1/2 of urn. Peristome red-brown, to 200 µm long, cribrose along median line near the apex, papillose to vertically striate-papillose. Exothecial cells to 25 µm wide, not in regular vertical rows, quite irregular in size and shape, rectangular 2–4: 1, rather thick walled. Stomata phaneroporous, restricted to base of urn. Spores smooth, to 12 µm.
| Literature | Greven 2003; Koch 1950a, 1958; Koch and Ikenberry 1954; Lesquereux 1868; Lesquereux and James 1884; Muñoz 2000; Showers 1982; Spjut 1971; Watson 1880. As Grimmia brevirostris Koch 1950a, 1958; Williams 1920. |
| Illustrations | Malcolm et al. 2009 p. 63; Greven 2003. |
| Bioregions | CaR, SN, SNE. |
| Vouchers | Fresno Co.: below Kearsarge Pass, South Fork Kings River, Kings Canyon National Park, Shevock 14329; Inyo Co.: slopes above Treasure Lake west of Big Pine, John Muir Wilderness, Inyo National Forest, Norris 47005; Mariposa Co.: Yosemite Valley, ledges near Wawona Tunnel, Yosemite National Park, Flowers 5413 (MO) [determined by Muñoz]; Nevada Co.: trail from Donner Rest Area to Summit Lake, Tahoe National Forest, Whittemore 3042 & 3045 (MO) [determined by Muñoz]; Tulare Co.: Sawtooth Pass Tail, Mineral King, Sequoia National Park, Shevock & O'Brien 16026 (determined by Muñoz). |
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