Salvinia molesta

Copyright Larry Maupin 2003 All Rights Reserved
Click images to enlarge

Colonizing Stage
It appears as just another water plant, floating loosely and freely (it is a true floater). It multiplies very rapidly in warm, nutrient-rich, still water.

Intermediate stage
As the population grows, it spreads over the water until the surface is
covered. At this point is begins to increase in depth and may become up to two feet thick due to wind and wave action.

Mat-forming stage
As the population becomes more dense, the form of the plant changes from a flat set of leaves to an upright form with undulating layers of foliage, as shown in the close-up photo below

Excerpt from

By Larry Maupin

Consider the effects of just one invasive plant, giant salvinia (Salvinia molesta). There are other "baddies," like water lettuce (Pistia stratiotes) and water hyacinth (Eichhornia crassipes), but giant salvinia is the newest and baddest bully on the block. It is technically an aquatic fern native to the river systems of southern Brazil. From there it has spread to South Africa, Australia and the United States. The U. S. Army Corps of Engineers' Aquatic Plant Control Section in Jacksonville, Florida believes the plant "was most likely introduced through the aquarium and landscape trades." Many folks enjoy their plants and fish until they are no longer able to care for them, then they decide to "set them free." Dr. R. Michael Smart, head of the U. S. Army Corps of Engineers' Aquatic Ecosystem Research Facility in Lewisville, Texas provides a succinct alternative: "Don't dump what you are tired of - destroy it." With no native predators or pests to check their growth, giant salvinia and other aquatics can spread quickly.

Invasive species use up nutrients that other species rely on, and their rampant vegetation blocks sunlight and destroys fragile environments. Fish won't eat it and it forms dense mats of foliage that choke out other aquatic plants. Wind and wave action can cause it to form mats up to three feet thick; then when the thick mats die of starvation, the decaying plant material robs the water of oxygen, killing all aquatic creatures.

Excess vegetation also ruins the waterway for recreation, fishing and navigation, while the pond or lake takes on the look of newly mowed pasture - acres of greenery.

Giant salvinia has been called "possibly the worst weed in the world" due to its aggressive growth -- it can double in quantity every 2.2 days under ideal conditions. That means that one plant becomes 8000 in 30 days! (Don't believe it? Do the math.) In two months the number is in the millions - clearly not a plant you would want roaming free in your waterways.

Thriving ecosystems can be reduced to monocultures of giant salvinia. In much of the world it is known as Karaba weed, for it inundated the entire Karaba Lake in Zimbabwe, Africa, within only a few years. Can you imagine a single species of floating plant covering 96 square miles of water? So, throwing an aquatic plant into a stream is akin to tossing a Styrofoam cup out of a car window, except that the cup can grow to 8000 cups in a month. And each of them can produce 8000 more!

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