Plants of this species are easily identified by the numerous clavate to subround gemmae, with transverse and longitudinal septa, on the stems and rhizoids. The narrower leaves with acute to acuminate, apiculate apices and the gemmae characters separate Z. erosus from the closely related Z. trichomitrius.
Plants medium-sized to large, caespitose, yellowish green to green above, yellowish brown to brown below; corticolous. Stems up to 50 mm tall, branching dichotomously or by subperichaetial or subperigonial innovations, tomentose below; rhizoids smooth to coarsely papillose, reddish brown to red; in section weakly pentagonal to subround, inner cortex 6-12 cells across, thin-walled, outer cortical cells smaller, in 2-4 rows, incrassate or consisting of stereids. Leaves crowded, ± equal in size to larger above, twisted or contorted when dry, erect-spreading to squarrose and reflexed to recurved when wet, frequently rugulose, frequently in 5 indistinct rows, spiralled around stem; narrowly ovate-lanceolate to oblong-lanceolate or linear-lanceolate, 1.9-3.6 mm long; ventral surface keeled; apex acuminate, acute or occasionally obtuse, apiculate, cells of apiculus elongate, smooth, incrassate, frequently with single tooth; base scarcely differentiated, ± sheathing, margins decurrent; margins plane, generally crenulate, unistratose. Costa ending below apex or merging with elongated cells of apiculus; ventral and dorsal superficial cells long-rectangular to linear; in section subround, bulging dorsally, lamina ventrally inserted, 2 guide cells exposed ventrally, ventral stereid band absent, dorsal stereid band 1-4 cells thick, dorsal surface cells not differentiated, rough. Upper laminal cells irregularly rounded-hexagonal, ± flat, 8.5-12.5(-15.0) µm, papillae low, scattered; basal cells rectangular, thin-walled to incrassate, smooth or walls papillose, occasionally reaching higher along costa. Gemmae numerous, on stem and rhizoids, clavate to subround, with transverse and longitudinal septa, reddish brown. Dioicous. Perigonia terminal, quickly lateral by subperigonial innovation; leaves ovate or shortly ovate-acuminate. Perichaetia terminal, leaves scarcely differentiated. Seta 7-14 mm long, yellowish or brownish. Capsule cylindrical or narrowly pyriform, yellowish or brown, plicate, mouth sulcate dry, reddish brown, urn 1.5-1.8 mm long, neck 0.5 mm long; exothecial cells irregularly quadrate to rectangular, smaller at mouth, longitudinal walls incrassate above; annulus apparently absent. Peristome absent. Operculum 1 mm long, oblique. Calyptra 2.4 mm long, hairy, hairs ascending, uniseriate, smooth, cells smooth. Spores 16-20 µm, papillose.