Plants: delicate, in creeping mats. Stems: with branches 0.4–0.6 mm, 0.7–1 mm across leafy branch, main stem and branches arching upward, stem and branch apices with penicillate group of abruptly imbricate leaves. Leaves: 0.5–0.7 mm; margins incurved distally to form tubulose apex; supra-alar cells short. : Specialized asexual reproduction rare, by filamentous gemmae. Perigonia: on branches. Perichaetia: on stems or branches. Seta: red. Capsule: 0.4–0.6 mm; annulus absent; exostome teeth 16, lanceolate, finely striate, longitudinally furrowed; endostome basal membrane wide, segments equal to exostome teeth length, cilia 1, short, occasionally rudimentary. Calyptra: smooth. Spores: spheric, 13–14 µm, slightly roughened. Phenology: Capsules mature summer.

Rotten logs, tree bark, charred wood, moist live-oak hammocks. low elevations (0 m). Fla.

Distinctive gametophytic traits of Acroporium smallii include long-ovate leaves with erect margins, linear medial laminal cells, and alar cells much inflated and sharply differentiated from more distal cells. The species is confined to Miami-Dade County.