Plants small, floating aquatics. Stems creeping, branched, bearing hairs but no true roots. Leaves in whorls of 3, with 2 leaves green, sessile or short-petioled, flat, entire, and floating, 1 leaf finely dissected, petiolate, rootlike, and pendent. Submerged leaves bearing sori that are surrounded by basifixed membranous indusia (sporocarps); sporocarps of 2 types, bearing either megasporangia that are few in number (ca. 10), each with single megaspore, or many microsporangia, each with 64 microspores. Spores of 2 kinds and sizes, both globose, trilete. Megagametophytes and microgametophytes protruding through sporangium wall; megagametophytes floating on water surface with archegonia directed downward; microgametophytes remaining fixed to sporangium wall.
PLANT: Annual or perennial floating aquatic herbs, sometimes stranded on mud, heterosporous. ROOTS: absent. STEMS: usually pinnately branched, often breaking apart with age, with multicellular hairs. LEAVES: in whorls of 3 per node; dimorphic, 2 of them floating, green, the other submersed, nonphotosynthetic. FLOATING LEAVES: sessile or short-petiolate, simple, the venation densely reticulate without free included veinlets, the abaxial (submersed) surface with multicellular hairs similar to those of the stem especially in the proximal portion, the adaxial (emergent) surface with dense, complex, branched multi-cellular hairs consisting of a main column (interpreted as a papilla by some authors) terminated with 4 multicellular branches. SUBMERSED LEAF: short- to long-petiolate, dissected into a root-like network of fibrous veins. SORI: borne in sporocarps on short stalks along the submersed leaf. SPOROCARPS: of 2 types on the same plant, each consisting of sporangia enclosed in a membranous indusium, some of these with 10 or more megasporangia, each containing 1 megaspore, others with numerous microsporangia, each with 64 microspores. SPORANGIA: thin-walled, lacking an annulus, breaking open irregularly through decay. SPORES: trilete, globose, relatively smooth-walled, megaspores large (0.3-0.5 mm) much larger than the dustlike (18-32mm) microspores. GAMETOPHYTES: reduced, developing inside the spores, the archegonia and antheridia protruding from the spore wall. X = 9. NOTES: 1 genus, ca. 10 spp., mostly tropical, N. Amer. to S. Amer., Eur., Asia, Afr. REFERENCES: Yatskievych, G. and M.D. Windham. 2008. Vascular Plants of Arizona: Salviniaceae. CANOTIA 4 (2): 46-49