Salvinia

Salvinia, a genus in the Salviniaceae family, is a floating fern named for Anton Maria Salvini, an Italian scholar from the 17th century. Salvinia is frequently referred to as watermoss.  In 1754, Jean-François Séguier wrote Plantae Veronenses, a description of the plants found around Verona. There are twelve known species, at least three of which (S. molesta, S. herzogii, and S. minima) are suspected to be hybrids, in part due to the presence of empty sporangia.

Salvinia is linked to other water ferns, such as the Azolla mosquito fern. Both Azolla and Salvinia are now included in Salviniaceae, despite the fact that each genus was previously assigned to its own family.

Salvinia, like the other ferns in the order Salviniales, produces spores of varying sizes. However, Salvinia’s leaf development is unique. The upper side of the floating leaf is morphologically abaxial, since it seems to face the stem axis. 

From a human perspective, when plants develop rapidly, they provide a specific hazard on lakes. For instance, they drained a large portion of Lake Bottineau near Doyline in Webster Parish, Louisiana, and impacted another Webster Parish location, Caney Lakes Recreation Area.

Habitat

Salvinia molesta is found in rivers, streams, lakes, dams, swamps, irrigation channels, drainage lines, and other bodies of water around the world. It is also a pest of paddy rice fields. It is mostly a tropical, subtropical, and warmer temperate weed.

Morphology 

Aquatic plants with little, creeping stems that are branching and contain hairs on the leaf surface papillae but lack actual roots. Two leaves are green, sessile or short-petioled, flat, whole, and floating, while one leaf is finely dissected, petiolate, rootlike, and pendant. Sori-bearing submerged leaves enclosed by basifixed membranous indusia (sporocarps).

They produce sporocarps of two types: either a few megasporangia (about ten), each with a single megaspore, or a large number of microsporangia, each with 64 microspores. Spores come in two shapes and sizes: globose and trilete. Megagametophytes and microgametophytes protruding through the sporangium wall; megagametophytes floating on the surface of the water with archegonia pointing downward; microgametophytes staying attached to the sporangium wall.

The little, hairlike growths, referred to as trichomes or microgametes follicles, have no recognised productive function and remain a biological mystery.

Salvinia molesta

Reproduction and dispersal

This plant reproduces vegetatively, with the floating branches quickly dispersing to generate new plants. Individual plants (ramets) can be as simple as a stem with two floating ‘leaves’ (fronds) and a third ‘leaf’ that has been transformed into feathery ‘roots’ and is submerged. These plants are dispersed during floods, as well as through water movement induced by currents or wind, and by the dumping of pond debris. Additionally, it can be spread by animals (especially long-distance aquatic birds), automobiles, and boats. 

Salvinia effect

The Salvinia effect is a term that refers to the permanent stabilisation of an air layer atop a hierarchically structured submerged surface. Based on biological models (for example, the floating fern Salvinia and the backswimmer Notonecta), biomimetic Salvinia-surfaces are employed as drag-reducing coatings (up to a 30% reduction in drag was previously measured on the initial prototypes). When applied to the hull of a ship, the coating enables the vessel to float on an air layer, thereby lowering energy consumption and emissions. 

These surfaces require an extremely water repellent super-hydrophobic surface and a millimetre-scale elastic hairy structure to trap air while immersed. Since 2002, the Salvinia impact has been explored on a variety of plants and animals by biologist and botanist Wilhelm Barthlott (University of Bonn) and his colleagues. 

Between 2006 and 2016, publications and patents were filed. The finest biological analogues are floating ferns (Salvinia), which have extremely complicated hierarchically structured hairy surfaces, and back swimmers (e.g., Notonecta), which have a complex double structure of hairs (setae) and microvilli (microtrichia). Three of the ten known Salvinia species exhibit a perplexing chemical heterogeneity: hydrophilic hair tips, in addition to the superhydrophobic plant surface, contribute to the air layer’s stabilisation.

Environmental and other impacts

Salvinia molesta grows swiftly and can quickly cover the whole surface of (small and medium-sized) bodies of water with a dense mat of plants, obliterating any submerged plant life. Infestations that are dense can also obstruct oxygen exchange and light availability in the water column below, lowering water quality, killing primary producers, and altering the freshwater food chain. Dense mats obstruct navigation, fishing, and leisure activities and serve as hatching grounds for malaria and bilharzia vectors.

S. molesta has been classified as an invasive species by the Global Invasive Species Database (GISD 2010). It is classified on the United States’ Federal Noxious Weeds List and has been designated a noxious weed in South Africa (prohibited plants that must be controlled). They provide no economic function and have detrimental features for humans, animals, and the environment) and in all Australian states.

Economic impacts

In warm areas, giant salvinia (Salvinia molesta) is a frequently introduced invasive weed. It is a fast-growing plant that creates dense mats over calm waters. It is a South American native. Cyrtobagous salviniae, a tiny weevil, has been successfully utilised to manage gigantic salvinia. A possible use is the hydrophobic trichomes, which do not repel oil. This qualifies them for oil spill cleanup, as they become saturated with oil in thirty seconds. S. molesta trichomes served as a basis for a synthetic polycarbonate that is similarly hydrophobic.

Legislation

Salvinia molesta has been designated a noxious weed in Kenya under the Noxious Weeds Control Act (CAP 325). The Minister of Agriculture has the authority under this act to require landowners who have such declared noxious weeds growing on their property to remove or have them removed. However, Uganda and Tanzania have not declared this species.

Conclusion 

Salvinia molesta is a free-floating aquatic plant that is indigenous to southern Brazil. It has grown rapidly over the last 50 years around the world and is invasive in a range of aquatic ecosystems, including lakes, rivers, and rice paddies. S. molesta is a close second to water hyacinth in terms of environmental, economic, and human health implications on a list of the world’s most noxious aquatic weeds. Additionally, it was recently included on a list of the world’s top 100 invasive species.