Salvinia molesta
| Giant salvinia | |
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| The fern Salvinia molesta floating on a pond surface | |
| Scientific classification | |
| Kingdom: | Plantae |
| Division: | Pteridophyta |
| Class: | Polypodiopsida/Pteridopsida (disputed) |
| Order: | Salviniales |
| Family: | Salviniaceae |
| Genus: | Salvinia |
| Species: | S. molesta |
| Binomial name | |
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Salvinia molesta D.Mitch. |
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Salvinia molesta, commonly known as giant salvinia or kariba weed after it infested a large portion of the reservoir of the same name, is an aquatic fern, native to south-eastern Brazil. It is a free floating plant that does not attach to the soil, but instead remains buoyant on the surface of a body of water. The fronds are 0.5–4 cm long and broad, with a bristly surface caused by the hair-like strands that join at the end to form eggbeater shapes. They are used to provide a waterproof covering. These fronds are produced in pairs also with a third modified root-like frond that hangs in the water.
Salvinia molesta is a complex of closely related floating ferns; they can be difficult to distinguish from each other. This water fern is often grown as an ornamental plant but has escaped and become a noxious pest in many regions worldwide. There are a few different growth forms for S. molesta. The primary growth form is an invading form with small flat leaves to the tertiary or mat form with large, crowded, folded leaves. Under the best conditions plants can form a two-foot-thick mat. These mats can put a halt to recreational activities on lakes and waterways. S. molesta has been used to extract nutrients and pollutants from the water. When this plant is dried out, it is used as satisfactory mulch.
Salvinia molesta prefers to grow in slow-moving waters such as those found in lakes, ponds, billabongs (oxbows), streams, ditches, marshes, and rivers. It prefers nutrient-rich waters such as those found in eutrophic water or those polluted by waste water. It does not usually grow in brackish or salty waters, but has been reported in streams with a tidal flow in southeast Texas. It copes well with dewatering, and while it prefers to grow in moderate temperatures, it will tolerate low or very high temperatures. The United States Geological Service believes that it could grow in zones 7a, 8, 9, and 10 of the USDA Plant Hardiness Map.
Environmental conditions can have a large impact on this plant. S. molesta can survive on a mud bank for a short period of time, but because of the dry conditions it cannot live there permanently. It grows best at a pH of 6–7.7 and at a water temperature of 20–30 °C. Growth can be increased in high light intensities. S. molesta cannot grow in high salt concentrations; the increase in salt causes a decrease in chlorophyll.
The plant originated in southeast Brazil and was exported as part of the pet industry to be used in aquaria and garden ponds. From there, it escaped or was deliberately released into the wild. It may also have been brought in with fresh, iced fish. Once in a waterway, it can be spread by infested boats which not only spread it to new areas, but also break the plant up which allows it to propagate. It also is spread by waterfowl.S. molesta has been spread by contaminated aquatic plant stocks, boats, and other watercraft. The movement of water spreads S. molesta and the sale and exchange of S. molesta materials increases chances of release to the environment.
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Wikipedia