Gametophytes bud-like, to 2 mm high, with unbranched, very short stems, scattered to gregarious, with conspicuous bright green protonemata at least when young. Leaves brownish and essentially echlorophyllose, concave, erect to erect spreading, ovate to oblong lanceolate with narrow but blunt apices, to 1.5 mm long, about 3: 1, little changed upon drying. Median laminal cells irregularly rectangular, 3–6: 1, smooth, moderately thick walled but without pitting, to 30 µm wide. Basal and alar cells shorter and broader than median cells. Margins plane, entire throughout or with distant teeth near the apices. Costa percurrent to subpercurrent, flattened and weak to missing near base. Axillary hairs to 5 cells long, to 150 µm, with one basal brown cell, not offset from leaf insertion. Rhizoids dense at least near base of plant, smooth, red-brown, repeatedly branched. Gemmae occasionally present on rhizoids, spherical and multicellular, usually green.
Dioicous or perhaps rhizoicous with male gametophores scattered among the females, often very difficult to find. Perichaetia mostly rather difficult to differentiate from the remainder of this very reduced plant. Seta pale to red brown, smooth, erect, to 25 mm long. Urn to 0.8 mm long, nearly spherical, erect to inclined, wrinkled but not regularly sulcate. Operculum flat but with a short apiculus. Annulus well demarcated, of 1–2 rows of thin walled, enlarged cells which fragment after capsule dehiscence. Exothecial cells at middle of urn isodiametric, quadrate to hexagonal, 5:1, to 20 µm broad, in regular rows, thick walled and frequently so densely verruculose as to obscure the cell outlines. Exothecial cells at capsule mouth smaller and thicker walled, often transversely elongate in 3–5 rows. Stomata absent. Exostome red brown to purplish, to 200 µm long, perforate along the median line, vertically to spirally striate dorsally, with high ventral lamellae. Endostome segments opposite and somewhat shorter than the exostome teeth, closely adhering to those teeth or distally flexed, with high and blunt papillae, about as long as exostome. Calyptra cucullate, sheathing developing capsule but later with its base adhering in a collar around the seta below the capsule. Spores spherical, to 25 µm, smooth to lightly papillose.
Discelium nudum is not uncommon on seaward facing bluffs of eroded clay usually within sight of the ocean in Northern California. In most of my collections it was scattered among various other small mosses, primarily Pohlia. In such conditions, it may be very difficult to recognise, and one must look for the small, almost globose, inclined to erect capsule on an erect, reddish seta. It occasionally grows in nearly pure colonies, and can then be recognised by the extremely reduced gametophyte which is almost without a stem and has only a few scale-like leaves.