Quick Facts

  • Free floating aquatic fern consisting of a horizontal stem lying just below the water surface that produces a pair of floating leaves and a highly dissected submerged leaf at each node
  • Individual leaves can range from a few millimeters to 4 centimeters long

Species Facts:

Giant salvinia is a fast-growing fern that can clog ponds and lakes. It represents a significant danger in any warm, slow-moving bodies of water. Forming mats up to 2 feet thick, the plant gobbles up oxygen and nutrients, and blocks sunlight needed by other water dwellers. When conditions are right, salvinia's small, oval leaves form dense mats - green, yellow-green, or brown - that can easily double in size in just a few days. A single plant has been described to cover forty square miles in three months! It ruins conditions for fishing, boating, and waterskiing. The weed also clogs irrigation and electrical generating systems. Giant Salvinia is federally prohibited in the US, and is therefore illegal to sell or possess.

During early stages Giant savlinia plants are smaller and leaves lie flat on the water surface. As the plants grow, the 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. Young, unfolding leaves will reveal fresh hairs that remain descriptive for the species. Submersed leaves are filamentous, look like roots, and often bear chains of egg-shaped sporocarps. Plants may demonstrate variability in the arrangement of the sporocarp chains, a function of developmental stage or a response to environmental conditions. Mature plants can produce large quantities of sporocarps that contain many sporangia, yet plants are functionally sterile.

Giant salvinia reproduces very effectively through vegetative means. Stems fragment as plants mature and new plants develop from apical and lateral buds. Each node harbors up to five serial lateral buds (Lemon and Posluszny 1997), adding to the species' high potential for growth and dormancy. Plants will withstand periods of stress, both low temperature and dewatering, as dormant buds.

Four species of Salvinia (S. auriculata, S. biloba, S. herzogii, and S. molesta) share the feature of egg beater-like hairs. All can be expected to be aggressive weeds and all four are prohibited as Federal Noxious Weeds. Of the four with egg beater-like hairs, only S. molesta is presently being found in the United States.

Image of Giant Salvinia in the water (Photo from: www.bugwood.com Credit to: Scott Robinson)