Salvinia

Lore & Background

The genus Salvinia was named in honor of 17th-century Italian naturalist Anton Maria Salvini, and the name was first published in 1754 by French botanist Jean-François Séguier in Plantae Veronenses. Twelve species are recognized, at least three of which—S. molesta, S. herzogii, and S. minima—are believed to be hybrids, in part because their sporangia are found to be empty. Salvinia is related to other water ferns, including Azolla; recent sources include both genera in Salviniaceae, though each was formerly given its own family.

Salvinia, like other ferns in the order Salviniales, is heterosporous, producing spores of differing sizes. However, leaf development in Salvinia is unique: the upper side of the floating leaf, which appears to face the stem axis, is morphologically abaxial. The plants are small, free-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 bear sori surrounded by basifixed membranous indusia (sporocarps).

The sporocarps are of two types: megasporangia, few in number (approximately 10), each with a single megaspore, or many microsporangia, each with 64 microspores. Spores are of two kinds and sizes, both globose and trilete. Megagametophytes and microgametophytes protrude through the sporangium wall; megagametophytes float on the water surface with archegonia directed downward, while microgametophytes remain fixed to the 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.

Reader's Guide

Salvinia is significant for its ecological and economic impacts, as well as for a unique physical phenomenon. Giant salvinia (Salvinia molesta) is a commonly introduced invasive weed in warm climates, native to South America, that grows rapidly—up to two times its dry weight in 2.5 days—and forms dense mats over still waters. Biological control has been achieved using the tiny weevil Cyrtobagous salviniae. A proposed use takes advantage of the hydrophobic trichomes, which do not repel oil, making 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.

The salvinia effect, discovered on Salvinia molesta by botanist Wilhelm Barthlott and described with physicist Thomas Schimmel, fluid mechanist Alfred Leder, and colleagues in 2010, describes the stabilization of an air layer upon a submerged hydrophobic surface by hydrophilic pins. This physicochemical phenomenon has implications for materials science. The geography of Salvinia fossil material suggests members of the genus may have been broadly distributed during the Tertiary. Its distribution is mostly tropical, across North America, Mexico, West Indies, Central America, South America, Eurasia, and Africa, including Madagascar, South Borneo, and Asia.

Did You Know?

• Salvinia cucullata is one of only two fern species for which a reference genome has been published.
• The salvinia effect, discovered on Salvinia molesta, describes the stabilization of an air layer on a submerged hydrophobic surface by hydrophilic pins.
• The trichomes of Salvinia molesta can become saturated with oil in thirty seconds and served as a model for a synthetic polycarbonate.