Salvinia

Stems with many multicellular hairs. Leaves horizontally spreading. Blades of floating leaves green and pubescent abaxially (on side away from water). Sporocarps borne on chainlike or cymelike organs or submerged leaves; sporangia indehiscent, dispersed as units when sporocarps decay.

Leaf development in Salvinia is unique. The upper side of the floating leaf, which appears to face the stem axis, is morphologically abaxial (J. G. Croxdale 1978, 1979, 1981).

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. 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