Giant Duckweed is identified by a dense canopy of tiny greenish plants growing in one or multiple layers on still or slow-moving water
Why the bad press? Because Salvinia Molesta, aka Giant Salvinia, does in fact sort of bully the environment it lives in. It is an aggressive weed that grows fast and is not satisfied by totally covering a water body in a mat of itself. Instead, once it has formed a dense floating mat on the surface, it proceeds to add a layer after another on top of the first layer, to form a multi-layered canopy that can reach as high as 1 meter.
And how does this molesta weed look like? It is a free floating, green plant that is typically seen in tightly packed canopies over water. It is difficult to identify one plant in that mass of weeds, but if you had to, the distinctive characteristic is that each plant has three leaves, two of which look normal greenish, rounded or broadly elliptical and about 2 cm long. The third leaf is odd. It dangles into the water, like an unsuccessful root, and is finely dissected.
Do not look for flowers among Giant Salvinias. The weed is a fern rather than a normal plant. A fern is a flowerless plant that has feathery leaves that are not just leaves but also reproductive organs as in, the underside of these leaves produces spores. A frond is what botanists call that sort of leaf.
The Giant Salvania is an immigrant weed in the US. It originally belonged to southeastern Brazil and northern Argentina, but found its way to most tropical and sub-tropical regions of the world, including most of the US.
True to its origin, the weed prefers warm temperate areas and grows best in still or slow-moving water such as ponds, lakes, ditches, slow-moving rivers and canals. But it is also quite adaptive and varies its size and structure to the available conditions, especially space and nutrients.
Besides using the spores to develop new plants, Giant Salvania also uses the conventional vegetative method of forming new plants from broken parts of the parent plant. And the weed grows very fast to dominate almost every water body that it finds itself in. That is perhaps where the weed's bad name becomes justified. In just about any water body it finds its way into, Giant Salvania quickly becomes a nuisance, disrupting habitats for water birds and fish and impeding commercial and recreational use of the water.
Physical or mechanical removal of the Giant Salvania weed is only effective in small water bodies and even then only has a temporary measure. But there are two more effective weapons against the weed.
The first is a biological weapon called Cyrtobagous Salvinae. That is a two-millimeter black beetle that is at home both in and outside water. This beetle happily eats its way through Giant Salvania and has been known to considerably slow down the weed. Removal with the DeSkuzzer is another way to get instant results.