Salvinia

Small, floating aquatics with creeping stems, branched, bearing hairs on the leaf surface papillae but no true roots. Leaves are in trimerous whorls, with two leaves green, sessile or short-petioled, flat, entire and floating, and one leaf finely dissected, petiolate, rootlike and pendent. Submerged leaves bearing sori that are surrounded by basifixed membranous indusia (sporocarps).

They bear sporocarps of two types, either megasporangia that are few in number (approximately 10), each with single megaspore, or many microsporangia, each with 64 microspores. Spores are of two kinds and sizes, both globose, trilete. Megagametophytes and microgametophytes protruding through sporangium wall; megagametophytes floating on water surface with archegonia directed downward; microgametophytes remaining fixed to sporangium wall.

The small, hairlike growths, known as trichomes or microgametical follicles, are not known to have any productive function, and are currently a biological mystery.

Phylogeny of Salvinia^[5][6]

Other species include:

• S. biloba Raddi
• S. ×delasotae Miranda & Schwartsburd 2019 {Salvinia sprucei × Salvinia minima}
• S. hastata Desvaux
• S. martynii Kopp
• S. nuriana de la Sota
• S. nymphellula Desvaux
• S. sprucei Kuhn

The geography of Salvinia fossil material suggests members of the genus may have been broadly distributed during the Tertiary.^[7][8]

Distribution is mostly tropical, in North America, Mexico, West Indies, Central America, South America, Eurasia and Africa, including Madagascar, South Borneo, Asia.

Giant salvinia (Salvinia molesta) is a commonly introduced invasive weed in warm climates, but is native to South America. It grows rapidly, up to two times its dry weight in 2+1⁄2 days, and forms dense mats over still waters. A tiny weevil, Cyrtobagous salviniae, has been used successfully to biologically control giant salvinia.^[9]

One proposed use takes advantage of the hydrophobic trichomes, which do not repel oil. This makes them candidates for mopping up oil spills, as they become saturated with oil in thirty seconds. S. molesta trichomes served as a model for a similarly hydrophobic synthetic polycarbonate.^[10]

The salvinia effect describes the stabilization of an air layer upon a submerged hydrophobic (water repellent) surface by hydrophilic (water loving) pins. This physic-chemical phenomenon was discovered on the floating fern Salvinia molesta by the botanist Wilhelm Barthlott (Universität Bonn) while working on the Lotus effect and was described in cooperation with the physicist Thomas Schimmel (Karlsruher Institut für Technologie), fluid mechanist Alfred Leder (Universität Rostock) and their colleagues in 2010.

• USDA
• Salvinia minima in Flora of North America
• S. molesta as pest