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Salvinia (a complex consisting of Salvinia auriculata Aubl., Salvinia biloba Raddi, Salvinia herzogii de la Sota, Salvinia molesta D.S. Mitch)
Common names: giant salvinia
Disseminule: Spores, stem fragments
Free-floating perennial aquatic ferns with stems just below water surface and floating leaves (fronds). Upper surfaces of floating leaves bear eggbeater-shaped hairs. Primary growth form has small, flat leaves; tertiary growth form is a mat of crowded, folded leaves.
Although the members of the Salvinia complex are difficult to distinguish, the eggbeater-shaped hairs are diagnostic for this group; the non-noxious Salvinias do not have them.
Widespread (particularly Salvinia molesta) throughout the tropics and subtropics, in South America, Africa, India, Southeast Asia, Australia, New Zealand, and the Pacific islands.
Native to tropical South America.
Tropical to warm-temperate climates, in still and slow-moving waters of ponds, rivers, marshes, and rice fields.
The Salvinia complex is a closely related group of floating ferns. S. molesta is the most notorious and widespread; originally used as an ornamental aquarium plant, it has now become naturalized worldwide. S. auriculata reportedly infests Lake Kariba in Africa and waters and rice fields in Sri Lanka. The tertiary growth form of these plants can very quickly form dense mats that may be more than 2 m thick. These mats block light and oxygen, displacing native plants. The mats also decrease water quality, and interfere with hydroelectric plants and recreational use. S. biloba and S. auriculata may produce fertile spores, but S. molesta and S. herzogii are sterile hybrids. The chief means of reproduction is vegetative. Buds form at stem nodes, and stem fragments are dispersed by wind, water currents, and human activities such as boating. Cyrtobagous salviniae is a weevil that has been used successfully to control S. molesta in several countries.