Salvinia Ség.
Descripción
Aquatic, floating on water; roots absent, their function perhaps taken by highly dissected submersed leaves resembling a cluster of roots; rhizomes horizontal, slender, branched, hairy, the nodes close or distant from each other; leaves not circinate in bud, in groups of three at a node, two floating, green, flattened, sessile or short-stalked, the third leaf submerged, pendent, root-like and functioning as a root, brownish, highly branched, the branches covered with dark septate hairs; floating leaves ca. 5–25 mm long, round to oblong, often cordate at base, entire, flat or somewhat folded upward, with a distinct midrib and reticulate veins, without included veinlets, adaxial surfaces bearing numerous hairs from the blades or from multicellular papillae, in groups of 4, abaxial surfaces with uniseriate, septate, brownish hairs; sporocarps of 2 kinds (heterosporous), in chain-like or cyme-like clusters on the submerged leaves (both kinds on the same submerged leaf), a few, basal megasporocarps and more numerous, distal microsporocarps, both kinds globose, ca. 1.5–2 mm diam., the wall membranaceous (interpreted as a 2-layered indusium), each sporocarp containing numerous sporangia (collectively, the sorus) lacking annuli; sporangia ovoid or pearshaped, with a highly vacuolate layer in which the spores develop; megasporangia to ca. 40 per megasporocarp, on branched or unbranched stalks, each producing 32 spores but only one maturing, this tetrahedral-globose, with a minutely perforate surface; microsporangia 100+ per microsporocarp, on slender branched stalks, each containing 32 or 64 tetrahedral-globose, rugulose microspores, these shed as a unit and embedded in the vacuolate tissue; x=9.A
Forma de vida
Hidrófita libreA
Distribución
México (país) Nativo y no endémicoA
Categoría IUCN
No incluidaB
Categoría NOM-059-SEMARNAT-2010
No incluidaC
Discusión taxonómica
Salvinia is a pantropical genus of about 11 species with seven species in America. All species occur in stagnant, nutrient-rich, freshwater lakes and pools, and in slow moving rivers, at low to middle elevations. The genus was monographed by Herzog (1935), and the Salvinia auriculata complex was studied by de la Sota (1976), Mitchell (1972), and Mitchell and Thomas (1972). Some species form extensive mats that may clog waterways. Salvinia molesta D. S. Mitch. is an aggressive and noxious weed in some areas, as evidenced by its rampant growth on the artificial Lake Kariba in Zambia and Zimbabwe (Mitchell, 1969, 1972; Moran, 1992). This species, demonstrating hybrid vigor and abortive spores, is postulated by Mitchell (1972) to be a hybrid of horticultural origin in South America which has now spread to Africa, Ceylon, Indonesia, Australia, and the United States.
Salvinia is related to Azolla, and the two genera (often treated in separate families) have been shown recently to be most closely related to the third (and only other) family of heterosporous ferns, the Marsileaceae (Pryer et al., 1995; Rothwell & Stocky, 1994). Salvinia is distinct by its floating habit, round to oblong vegetative leaves with compound hairs, and root-like leaves with sporocarps. Because of the habitat in which the plants are found, both the vegetative and the reproductive structures are highly modified and do not resemble those of other ferns. Fertile material is rarely seen. Fossils of the genus are known from the Upper Cretaceous.
A
Salvinia is related to Azolla, and the two genera (often treated in separate families) have been shown recently to be most closely related to the third (and only other) family of heterosporous ferns, the Marsileaceae (Pryer et al., 1995; Rothwell & Stocky, 1994). Salvinia is distinct by its floating habit, round to oblong vegetative leaves with compound hairs, and root-like leaves with sporocarps. Because of the habitat in which the plants are found, both the vegetative and the reproductive structures are highly modified and do not resemble those of other ferns. Fertile material is rarely seen. Fossils of the genus are known from the Upper Cretaceous.
A