Giant Salvinia   (Salvinia molesta) 

DESCRIPTION

Giant salvinia is free floating aquatic fern and has three leaves, two above water and the third submerged. Salvinia forms floating mats that shade and over crowd native plants thus, threatening water quality and the oxygen supply. These mats also form in rivers and irrigation ditches which constrains agriculture. These mats can clog drains, irrigation intakes and be snagged by boats and spread to other areas. Giant salvinia is consisting of a horizontal stem that floats just below the water surface and produces, at each node, a pair of floating leaves, ovate to oblong in shape, and a third leaf that is highly dissected and submersed. Plants are capable of several growth forms where individual leaves can range from a few millimeters to 4 centimeters long. During early stages plants are smaller and leaves lie flat on the water surface. As plants grow, leaves curl at the edges in response to self competition. Eventually a vertical leaf position is attained as mature plants press into tight chains and form mats of many floating plants. Leaf surfaces have rows of papilla (cylindrical stalks) branching into two to four hairs that rejoin at the tips to form an egg beater-like structure. This feature distinguishes S. molesta from common salvinia, S. minima, which has branched hairs that are spreading and free at the tips. Hairs on mature leaves may be damaged and not true to type, however, young, unfolding leaves will reveal intact hairs that are descriptive for the species.

Photo credit: Univ. of Florida & Center for Aquatic and Invasive Plants

(Source: 1. Giant Salvinia, USGS, http://salvinia.er.usgs.gov/ ; 2. Biological Control of Weeds: Department of Entomology, Texas A&M University, http://bc4weeds.tamu.edu/salvinia.html)

IMPACTS

Growth factors paired with features promoting mobility make Salvinia molesta an  aggressive, competitive species that can impact aquatic environments and local economies. Under favorable growth conditions plants may double within about one week. Live biomass weights approach those recorded for water-hyacinth. Excessive growth can result in complete coverage of water surfaces.  This degrades natural habitats in several ways. Heavy growth of giant salvinia competes with and shades desirable native vegetation. Mats of floating plants prevent atmospheric oxygen from entering the water, while decaying salvinia drops to the bottom, greatly consuming dissolved oxygen needed by fish and other aquatic life. 

Animal habitat is most noticeably altered by the obliteration of open water. Migrating birds may not  recognize or stop at waterbodies covered with giant salvinia. Indeed, the  resulting loss of open water in the Swinney Marsh region has prompted local  waterfowl guides to question the economic benefits of renewing hunting leases. There local fishermen have found it impossible to cast into water covered with dense mats of giant salvinia and are abandoning spots once fished for bass, crappie and sunfish.

Giant salvinia clogs water intakes to interfere with agricultural irrigation and electrical generation. Many infested farm ponds in Texas lie on creeks that drain important tributaries heavily depended on for agricultural irrigation.


(Source: 1. Giant Salvinia, USGS, http://salvinia.er.usgs.gov/html/identification.html)

Giant Salvinia: USGS
    http://salvinia.er.usgs.gov/
This site gives a description of News and Notes, United States Distribution, Cultivation, Predicted U.S. Range, Identification, Bibliography, and Submit Possible Sightings. 

Giant Salvinia: USDA 
    http://plants.usda.gov/cgi_bin/plant_profile.cgi?symbol=SAMO5
This site provides very detailed information about classification, plant distribution by state, and images.

Aquatic, Wetland and Invasive Plant: Particulars: Univ. of Florida & Center for Aquatic and Invasive Plants
    http://aquat1.ifas.ufl.edu/salmol.html
This site includes 12 useful photographs of giant salvinia.

Invasive Alien Species, Salvinia molesta: Department of Agriculture Invasive Alien Species
    http://www.agriculture.state.az.us/PSD/giant_sal1.htm
This site describes a general description, native range, expected US range, habitat, nonindigenous occurrences, status, and references about salvinia molesta.

Giant Salvinia: University of Arizona
    http://ag.arizona.edu/azaqua/extension/ANS/Salv4.htm
This site gives a brief description of giant salvinia in the State of Arizona.

Salvinia molesta: University of Florida Invasive Plant Alert
    http://aquat1.ifas.ufl.edu/salpage.html
This page contains a description of giant salvinia and pictures.

Alien Ferns in Hawaii
    http://www.nhm.org/research/botany/wilsonferns/sal_mol.html
This site explains an introduced history of Salvinia molesta in Hawaii and general description. 

Salvinia molesta: Pacific Island Ecosystems at Risk (PIER)
    http://www.hear.org/pier3/samol.htm
This page includes a general description, habitat/ecology, control, and references.

Southern Division of the American Fisheries Society
    http://www.sdafs.org/reservor/news/releases/salvinia.htm
This site gives the following descriptions with photos: Status, Problem, Characteristics, and Prevention.

Biological Control of Weeds: Department of Entomology, Texas A&M University
    http://bc4weeds.tamu.edu/salvinia.html
This site provides information about identification, biology, history, status, range, biological control agents (Salvinia weevil, Cyrtobagous salviniae, Salvinia Stem Borer, Samea multiplicalis), and links. 

Weed Alert, Giant Salvinia: The Nature Conservancy: Wildland Weeds Management & Research Program
    http://tncweeds.ucdavis.edu/alert/alrtsalv.html
This site provides descriptions of giant salvinia with photos, impacts and considerations, range as an invader, and references. 

  USDA ARS Agricultural Research Magazine
     http://www.ars.usda.gov/is/AR/archive/nov01/giant1101.htm
This site gives general description and a list of control methods with pictures.

Giant Salvinia: Western Aquatic Plant Management Society
    http://www.wapms.org/plants/index.html
This site includes a description and variation, economic importance, geographic distribution, habitat, reproduction, and references.

Status of Salvinia minima and S. molesta in the Southern United States

  Link

This article presents a chronology for early records on Salvinia minima, the geographic distribution of Salvinia minima, and the distribution of Cyrtobagous salviniae associated with Salvinia minima.