1. Acroporium smallii (R. S. Williams) H. A. Crum & L. E. Anderson, Bryologist. 63: 43. 1960.
Sematophyllum smallii R. S. Williams, Bryologist 23: 76, plate 6. 1920
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.
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.