Small, free-floating aquatic ferns, capable of rapid vegetative repodcution by fragmentation and forming a carpet on still water. Rhizome horizontal, zig-zag, freely branching atlernately to the left and right, bearing close, minute leaves and spaced simple roots, vascular system poorly developed, a medullated protostele. Leaves imbricate, alternate, deeply bilobed; the aerial lobe overlapping the rhizome, thick, papillose, with a basal cavity containing a sybiotic filamentous blue-green algae (Anabaena azollae); the submerged lobe thin-membranous, not papillose. Sporangis borne in sporocarps, usually paired micro- and megasporocarps, borne in the axils of the submerged lobes, basally on the branches, quite enclosed by a thin indusium; microsporocarp large, globose, containing several to many globose microsporangia, each containing 32 - 64 microspores; megasporocarp smaller, containing a single megasporangium with a single megaspore. Spores globose, trilete, smooth to variously pitted or sculptured; microspores imbedded in the outer edge of several mucilaginous masses (massulae) int eh microsporangium, the massulae bearing several to many, hooked (glochidiate) or non-hooked, septate or non-septate processes on one or all sides; megaspores with 3 or 9 apical massulae or "floats".
|A single species in Papuasia...||A. pinnata|