Salviniaceae — Floating Fern Family
This species of floating ferns consists of round or oval leaves (fronds), usually an inch long or less, borne in pairs along a slender stem, but often appearing congested and clumplike. The upper surface of the fronds is covered with very distinctive hairs borne on slender cone-like stalks, with four segments drawn together at the tips, that look like an eggbeater (seen with low magnification). Hanging from the plant are dark brown root-like structures, which are actually modified fronds, and strands of small, egg-shaped spore-bearing organs (sporocarps).
Salvinia molesta is native to Brazil, but widely naturalized, particularly in the tropics and subtropics of the Old World. In the United States, it is reported in states along the coast from Virginia to Texas, as well as in Arizona, California and Hawaii.
This species is not often found in the wild and has been documented in only two Florida counties: Bay and Collier. The fern is spread when cultivated plant material finds its way from aquaria to ponds, lakes, canals, swamps and slow-moving streams.
Salvinia minima is very similar in general appearance and occurs in similar habitats, but usually has smaller fronds, and the hairs on their upper surface are not like eggbeaters but rather have spreading tips. Until the late 1990s, this species was thought to be native to Florida, but research has demonstrated it is exotic and should be treated as a pest plant, as are other members of this genus.
This fern produces abundant spores, but primarily reproduces rapidly by vegetative means. Large clumps of the plant eventually break up and start new ones. Giant salvinia creates a dense cover on the water, blocking out sunlight for other aquatic organisms.
All exotic species of Salvinia are classified as Class I Prohibited Aquatics by the state of Florida (DPI Rule 5B-64). Most species are very similar to S. molesta, and many have the characteristic “eggbeater” hairs, but none are known to be present in the wild or in cultivation in Florida at the present time. In addition to S. molesta, the following closely related species are on the federal Noxious Weed List: S. auriculata, S. biloba and S. herzogii. Salvinia minima will eventually be added to the state of Florida’s list of Class I Prohibited Aquatics.