Scientific name: AzollaceaeEnglish name: Vietnamese name: Bèo hoa dâuOther name:
Small, floating herbs, often forming a mat over still waters, rhizome fins, horizontal, branching alternately to the left and right, bearing small, close leaves and fine, simple roots, protostelic. Leaves +/- imbricate, alternate, bilobed, papillose. Sporangia borne in sporocarps, in the axils of the submerged lobes of the leaves, enclosed in a thin indusium, the sporocarps of 2 types, microsporocarp large, with several microsporangia each with many microspores, megasporocarp with a single megasporangium with an single megaspore; spores globose, trilete.
A mongeneric family with about 6 species, found throughout the tropical and temperate regions of the world. Azolla pinnata is the only species in Papuasia.
Small, free-floating aquatic ferns, capable of rapid vegetative reproduction by fragmentation and forming a carpet on still water. Rhizome horizontal, zig-zag, freely branching alternately 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 symbiotic filamentous blue-green algae (Anabaena azollae); the submerged lobe thin-membranous, not papillose. Sporangia borne in sporocarps, usually paird micro- and megasporocarps, borne in the axils of the submerged lobes, basally on the branches, quite enclosed by a thin indusium; microsporocarp large, gobose, 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) in the microsporangium, the massulae bearing several to many, hooked (glochidiate) or non-hooked, septate or non-septate processs on one or all sides; megaspores with 3 or 9 apical massulae or 'floats'.