Salvinia molesta Mitchell

Aquarium Water-moss, Giant Salvinia

Threat Level	Category
Emerging	Aquatic

Description

Stems

Stems or rhizomes are horizontal and float at or just below water surface.

Leaves

Leaves or fronds are paired and develop at each node of the rhizome. They are bright green, oval, and have a mid-rib with numerous stiff white hairs. The hairs form a cage-like structure, which is definitive for the species.

This water moss has no roots, but has delicate, finely dissected submersed fronds, which are brown and resemble roots.

Reproduction

This plant does not flower. Sporocarps are borne in chains or clusters on submersed stalks; however, these are not fertile. Reproduction is by vegetative fragmentation or new plants from lateral and terminal buds.

Images

Photo: Forest & Kim Starr, U.S. Geological Survey, Bugwood.org
More images of Salvinia molesta

Life History

Giant Salvinia, is a floating aquatic fern native to Brazil which was brought to the United States as ornamentals or through the aquatic plant industry. It is highly invasive and as infestations grow in size the plant forms mats of floating plants. These mats can reach three feet in thickness, blocking sunlight and oxygen from the water below. In ideal conditions a single plant can form a mat covering several entire water surfaces of ponds and waterways. These mats can serve as colonization points for grass and trees, forming floating islands.

Habitat

Will grow in lakes and ponds, oxbows, ditches, slow-flowing streams and rivers, marshes, and rice. Giant Salvinia favors water with a high nutrient content. It does not usually colonize brackish or marine environments. While moderate temperatures between 40 degrees and 90 degrees Fahrenheit are required, Giant Salvinia has survived severe winters.

Origin and Distribution

Giant Salvinia is a floating aquatic fern native to Brazil which was brought to the United States as ornamentals or through the aquatic plant industry. It is currently found in at least 12 southern states from California to North Carolina.

Management Recommendations

Mechanical Control

Hand removal is practical only for small infestations. Harvesting equipment has been used with some success, but this is less effective in shallow water. Mechanical removal is discouraged, as reproduction is by fragmentation, which is hard to avoid with mechanical removal methods.

Chemical Control

Giant Salvinia is susceptible in varying degrees to herbicides including 2,4-D, hexazinone, diquat, ametryne, fluridone, and double chelated copper.

Biological Control

This option offers promise for reducing infestations. The Salvinia Weevil, Cyrtobagous salviniae, has been used with good success in Australia and South Africa. It has been found in several parts of Florida. It is very specific to Salvinia species, making introduction to other states promising.

Use of grass carp for control has limited success.