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| Giant Salvinia - Salvinia molesta |
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Taxonomy: Family-Salviniaceae; Division-Polypodiophyta (Pteridophyta), true ferns. Salviniaceae consists of the single genus Salvinia. About ten species of Salvinia occur worldwide, seven originate in the Neotropics. None are native to North America. Native Range: Localized area of northern Brazil, South America, in the states of Pará, Goyaz, Bahía and Minas Geraes (de la Sota, 1962). Description: Free floating aquatic fern developing from a somewhat zigzagged horizontal stem (rhizome) that floats just under the water surface. The rhizome bears opposite pairs of rectangular floating leaves and a third submersed, filamentous leaf along each node. The roots are absent, although the submersed leaf has a root-like look. Floating leaves are three times longer than wide, measuring about 2.7 to 4.2 cm long and 1.0 to 1.8 cm wide. They are positioned above a prominent keel of spongy aerenchyma tissue which aids in keeping the large leaves afloat. Floating leaves lie flat or can be folded on the mid-rib depending on the density of the population. Individual plants commonly grow 20 - 25 cm long, often resembling the size and shape of a loaf of bread. The long rectangular leaves and spongy keel are characteristic for this species. Nearly all parts of the plant, except the upper leaf surface are sparsely clothed in chestnut colored hairs. The upper leaf surface of Salvinia oblongifolia is covered with double rows of short, blunt papillae that appear as linear arrays of cone-like projections. With fresh leaves and high magnification (50-100X), the papillae can be distinguished as bearing 1 to 2 fine, straight hairs at the tip. These hairs turn brown and shrivel, or are completely destroyed with pressing and drying. Mature plants produce large quantities of sporocarps among the submersed leaves. Sporocarps are cylindrical sacs arranged on short stalks in compact bundles. The sporocarp sacs contain many sporangia which in turn contain the reproductive spores. Macrosporocarps bear female spores, and the more abundant microsporocarps contain male spores. Spores require water for dispersal and fertilization, and while it has not been studied in this species, sexual reproduction can be expected. Plants reproduce primarily by vegetative propagation. Vegetative multiplication is ensured by the fragile stems that continuously break apart. Every node along the rhizome bears at least one branch initial from which a new plant can arise. Comments: Salvinia oblongifolia appears to be much more sensitive to extremes in temperature and pH than either S. molesta or S. minima. In its native range, S. oblongifolia has been found to form dense, pure colonies in small, interior lagoons thriving at pH levels that vary between 5.5 and 6 (de la Sota, 1962). In cultivation, it is severely set back when temperatures drop below 50 degrees F. It is sometimes difficult to grow affected, perhaps, by fluctuations in pH. While Salvinia oblongifolia may not pose a threat to the temperate climates, it could be invasive in the frost free zones of the southern United States. This species is known in the United States only from cultivation. Salvinia oblongifolia is not listed as a Federal Noxious Weed; however, it is restricted by the few states that prohibit the sale of all species under the genus Salvinia. Authors: M.M. Richerson and C.C. Jacono References: Mitchell, D. S. and P. A. Thomas. 1972. Ecology of water weeds in the neotropics. A contribution to the International Hydrological Decade. 13-21. Sota, E. R. de la 1962. Contribucion al conocimiento de las Salviniaceae Neotropicales I. Salvinia oblongifolia Martius II. Salvinia auriculata Aublet III. Salvinia herzogii Nov. Sp. De Darwininiana. 12(3): 465-520. |
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