Salvinia molesta

Salvinia molesta, aka Kariba weed, is related to S. auriculata and may be the result of a hybridisation of various South-American Salvinia species in the Botanical Garden of Rio de Janeiro. It has been introduced into many tropical and subtropical regions of the world by human activities and is often considered an invasive aquatic weed.

Tropical S. molesta and maybe S. auriculata as well are often sold as aquarium or pond plant under the erroneous name Salvinia natans.
True Salvinia natans, however, is an altogether different species native to Europe and Asia. It is not available in trade. In Central Europe it is found in only a few locations, mostly in nutrient-rich, relatively warm waters like cut-off meanders of rivers. S. natans is a highly endangered species and is especially protected by law e.g. in Germany.

Salvinia molesta, as well as other forms of the group of Salvinia auriculata, has a hairy leaf surface. These hairs grow in groups on small nubs and have an egg whisk-like form (visible under a magnifying glass). This characteristic is the best way to discern this group from other floating ferns like S. minima and true S. natans. The hairs on their leaves are not bent.

To be continued...