It depends on whether noxious means the same that "Prohibited" means in Texas. If so I'm guessing that it would be illegal for any store to ship the plant across state lines. In Texas the fine is $2000 per stem. If you have 10 nice little Eichhornia crassipes floating in your koi pond you're liable for a $20,000 fine.
I just visited the new PetCo in Corpus Christi and besides their usual contingent of purple krinkle plants, they had a half dozen Pistia stratiotes ($12,000).