Photo credit: © Forest and Kim Starr, https://flic.kr/p/D6xbE2
Report this Species!
If you believe you have found this species anywhere in Pennsylvania, please report your findings to iMapInvasives by submitting an observation record.
Species at a Glance
Common salvinia, also called “water spangles,” is a small free-floating aquatic fern native to tropical America. It was cultivated in the United States for use in ornamental fish tanks and ponds, but escaped to invade a variety of aquatic habitats. Once introduced, it has the potential to completely cover waterways.
Leaves: Because it is a fern, leaves are referred to as fronds. Fronds are borne in threes with two floating fronds and a third submersed frond that is dissected into filaments. The paired floating fronds are rounded with heart-shaped bases and notched tips. Smaller fronds lie flat on the water’s surface, while larger fronds fold at a distinct midrib, giving them a “cup-like” appearance. Length ranges from 0.4-2.0 cm (0.2-0.8 in). Fronds grown in the shade remain broadly round and emerald green, while those grown in the sun become larger, and turn a rusty brown color. Floating fronds are covered with rows of white bristly hairs on top that branch out to create a water resistant shield. Long, chestnut colored hairs coat the underside of the floating fronds, submersed filaments, buds, and rhizomes.
Flowers: Salvinias are ferns and have no flower.
Spores: Spores are produced in nut-like sacs called sporocarps that are attached in spirals along the submersed filaments.
Stems: Horizontal branching rhizomes float just below the water’s surface and produce leaves at each node.
Common salvinia may be confused with giant salvinia (Salvinia molesta), but it is the smaller of the two species and is readily distinguished by the morphology of the frond hairs. In both plants, the hairs are split four ways; however, in giant salvinia the hairs come together at the tip to form a distinct “egg-beater” structure. Typically, mature fronds of giant salvinia are quarter to half-dollar size, about twice the size of common salvinia.
While commonly found growing on the surface of still or slow-moving ponds, small lakes, canals, and slow streams, this species can also be found in shallow backwaters of bayous, oxbows, ditches, cypress swamps, and marshes inhabiting water bodies with salinity levels as high as 4-7 ppt.
Common salvinia reproduces and spreads mostly by fragmentation. Any part of the rhizome that buds or breaks off can form into a new plant. These rhizomes can also lie dormant during periods of reduced moisture and cold and will sprout again when conditions are more favorable. While it does contain spores, these spores are thought to be sterile.
Native to Central and South America, common salvinia first appeared in the United States in the St. John’s River in eastern Florida where it is thought to have been introduced in the ballast water of transoceanic ships. It quickly expanded its range westward and northward and can be found in the Mid-Atlantic region in New York, New Jersey, and Maryland.
Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.
The exponential growth of common salvinia allows it to quickly clog waterways and restrict recreational activities. It has been recorded growing as long as 12 m (39 ft), blanketing waterways with mats up to 25 cm (10 in) thick. These dense mats block sunlight from reaching native species and decrease oxygen concentrations that can ultimately impact fish and other aquatic species.
Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).