The following exotic plants are prohibited in Texas:
Giant Duckweed, Spirodela oligorhiza
Salvinia, All species of genus Salvinia
Water hyacinth and Rooted Water hyacinth, Eichhornia crassipes and Eichhornia azurea
Waterlettuce, Pistia stratiotes
Hydrilla, Hydrilla verticillata
Lagarosiphon (African Elodea), Lagarosiphon major
Eurasian Watermilfoil, Myriophyllum spicatum
Alligatorweed, Alternanthera philoxeroides
Paperbark, Melaleuca quinquenervia
Torpedograss, Panicum repens
Water Spinach, Ipomoea aquatica
The reason is, of course, that these plants have become invasive pests in at least one of the Texas waterways. We have a number of lakes that are nearly impassable by boats because of Hydrilla and water hyacinth and water lettuce have become almost as much of a problem in our east Texas lakes as they are in Florida and the surrounding states.
For those of you in Florida...here's the list for you:
Salvinia, all species except Salvinia minima
Water hyacinth, all species of Eichhornia
Hydrilla (Florida Elodea), Hydrilla verticillata
Lagarosiphon (African Elodea), all species of
Lagarosiphon
Eurasian Watermilfoil, Myriophyllum spicatum
Alligatorweed, Alternanthera philoxerioides
Paperbark, Melaleuca quinquenervia
Water Spinach, Ipomoea aquatica
Australian Pine, Casuarina all species
Sawah Floating Rush, Limnocharis flava
Purple Loosestrife, Lythrum salicari
Monochoria hastata and M. vaginalis
Giant Sensitive Plant, Mimosa pigra
Nechamandra alternifolia
Wild Red Rice, Oryza rufipogron
Tropical Pickeralweed, Pontederia rotundifolia
Brazilian Pepper, Schinus terebinthifolius
Exotic Burrweed, Sparganium erectum
Water Aloe, Stratiotes aloides
Water Chestnut, Trapa all species
Hippo Grass, Vossia cuspidata
In addition....the following plants are also prohibited in Florida except that they can be grown in state-regulated nursuries and only for sale out of state:
Hygro, Hygrophila polysperma
Ambulia, Limnophila sessiliflora
Water Lettuce, Pistia stratiotes
NOTE: I do NOT see any mention of any species of Duckweed on this list.