( Salvinia molesta )
DESCRIPTION: Giant salvinia is a free floating aquatic fern. An individual plantlet consists of a horizontal stem that produces two floating leaves (fronds) up to 25 cm long and a highly dissected submerged frond up to 25 cm. The floating leaves are green, sessile to short petiolate, broadly ovate in shape with entire margins. The midrib extends from the base to the apex of the leaf. The upper surface of the floating fronds is covered with parallel rows of hairs that have a characteristic "cagelike" structure at the apex. When plants are young, these leaves are small and float on the water surface. As plants age, the floating leaves become crowded and fold against one another resulting in a more vertical leaf position. The brown, feathery submerged leaf resembles and functions as a root. This frond bears the sporocarps or spore forming structures. The globose sporocarps are densely hairy, short stalked and 2-3 mm in diameter. Spores are rarely formed and if present are deformed and infertile.
PATHWAYS/HISTORY: Salvinia molesta is native to southeastern Brazil. Introduction of the mat-forming fern is thought to have arisen from the water gardening and/or aquarium trade where plants are either sold directly or occur as contaminants in water garden stock. Infestations have been reported from several states including Texas, Alabama, Mississippi, Louisiana, Florida, Arizona, California, Georgia, North Carolina, South Carolina, and Hawaii. The predicted range of the plant in the U.S. approximates the current distribution of water hyacinth.
RISKS/IMPACTS: Giant salvinia can impact irrigation systems, navigable waters, fisheries, electric power production, and rice farming. Giant mats reduce light penetration and result in oxygen depletion. As light becomes limiting, it affects the growth and survival of phytoplankton and vascular plants. Oxygen depletion may be so severely reduced beneath a mat that it influences fish survival. Extensive mats may exacerbate a situation because they prevent water circulation and mixing.
MANAGEMENT: Preventing additional infestations is the best method for control. Although it may be removed by manual methods, once established, giant salvinia may reproduce at a higher rate than it can be removed. Since this species can reproduce by fragmentation, it is all but impossible to completely eradicate by manual removal. A biocontrol agent, a beetle (Cyrtobagous salviniae), may be effective in limiting impacts. However, chemical control may be the only viable option available for eradication.
WHAT YOU CAN DO: Do not intentionally plant this species in water gardens or in aquaria. Clean all equipment that comes in contact with waters thought to harbor this species. Do not take or move any aquatic vegetation.
PROFILE CREDIT: Judy Shearer, USACE - IMAGE CREDIT: USACE