1. Erpodium acrifolium Pursell, Bryologist. 69: 465. 1966.
Plants shiny, dark green, irregularly branched, branches ± erect, in loose mats. Leaves imbricate when dry, widely spreading when wet, not complanate, symmetric to ± asymmetric, 0.6-1.1 mm, ovate to oblong-lanceolate, subulate, subula hyaline, smooth to serrulate; laminal cells bulging, smooth, thin- but firm-walled, quadrate to oblate-hexagonal, 16-38 µm × 20-36 µm; marginal cells slightly smaller. Perichaetial leaves enlarged, sheathing. Seta short to virtually absent, 0.04-0.08 mm. Capsule immersed to emergent, yellow-brown, ovoid-cylindric, 0.9-1.1 mm, stomatose; annuli broad, 2-3 rows of ± quadrate cells wide, persistent; peristome absent; operculm erect-rostrate. Calpytra to 0.6 mm, smooth, plicate, plicae serrate. Spores 23-32 µm, minutely papillose.
Dry areas on bark of trees and rocks; low to moderate elevations; Tex.; Mexico (Sonora, Tamaulipas).
In general aspect, Erpodium acrifolium resembles E. beccarii G. Venturi, a wide ranging species found in Mexico but not known from the United States. Both species have subulate leaves. However, E. acrifolium has smooth laminal cells whereas the laminal cells of E. beccarii are pluripapillose.