Plants in nature red-brown, brick or rose red or occasionally blackened distally, red-brown to tan proximally. Stems 1-1.5 cm, central strand present. Stem leaves appressed when dry, spreading and not keeled when moist, monomorphic; ovate to ovate-lanceolate, adaxial surface broadly concave across leaf and sometimes narrowly channeled near apex, 1.2-1.5 mm; base weakly differentiated in shape, broadly ovate, sheathing at insertion; margins recurved in lower 2/3-3/4, minutely crenulate by projecting cell walls; apex acute to short-acuminate, occasionally broken off; costa percurrent, strong, often weakly spurred, without an adaxial pad of cells or this weakly developed, adaxial cells quadrate from apex to near insertion, in 6-10 rows, guide cells in 2 layers; basal laminal cells not differentiated or of 2-5 rows of slightly larger cells, walls of basal cells evenly thickened, quadrate to short-rectangular; distal laminal cells 9-13 mm wide, 1:1(-2), often transversely elongate near proximal leaf margins, papillae of 2-4 hemispherical salients per cell or essentially absent and cells appearing broadly mammillose, lumens rounded-quadrate to ovate, walls evenly thickened and convex on both sides of lamina. Specialized asexual reproduction by fragile foliose stem tips. Seta 1. 1-1.4 cm. Capsule 1.5-2 mm; peristome teeth apparently absent or rudimentary. Spores 10-13 µm. Distal laminal KOH reaction deep brick or rose red.
Capsules mature May. Rock, outcrops, calcareous and volcanic boulders, fields, cliffs, runoff areas; low to moderate elevations (200-1500 m); B.C.; Calif., Oreg.
Didymodon norrisii is known only from four localities-California, one station each in Oregon and coastal British Columbia-and is quite distinctive. In addition to the characters given in the description, the leaves are reflexed above a very short-sheathing basal collar, the abaxial cells are quadrate in distal 4/5 of leaf, the costal transverse section is rounded-elliptical, the adaxial stereid band is absent, and there are 5-6 guide cells (4 in an abaxial layer and 1-2 in a second, adaxial layer). Sporophytes are uncommon, and the short-conic operculum is of cells in nearly straight rows.