Not exactly true, Arlene. The Federal Government actually lacks the jurisdiction to ban a plant within a given state (at least under these laws). There are no /federal/ laws prohibiting the possession or growth of Hygrophila polysperma or most other federally noxious weeds. However, it is illegal, under Federal law, to transport this plant over any state line, as well as to import it. These laws generally eliminate the trade of an organism within a given state; for example, it's technically legal in many states to buy, sell, trade, own, whatever snakehead (Maryland is NOT one of those states)... but, insomuch as there's no legal way to get one....
Each state has then the options to choose how to enact limiting laws on plants. In the case of Virginia, it is illegal to buy, sell, or trade Hygro. polysperma, (and possibly to possess it, I'd have to look up the laws again, and it's 1130). In Maryland, the law is a bit more complicated. There are a set of tiered levels of 'banned plants,' Tier 1 and Tier 2. Tier 1 plants may not be bought, sold, or traded under any circumstances, except as part of real estate. Propagation is also illegal, but is a vaguely defined term, at best. Tier 2 plants may be bought, sold, etc., provided any seller conspicuously notifies any purchaser of the possibility of this plant become invasive.
Bureaucracy at its best... they have been trying to come up with a list of plants for Tier 1 and Tier 2 since at least 2012. The website indicates that they expect to have an initial list up by June of 2015, but that list isn't up.
They've begun assessments of thirty or so species, but none of them are actually aquarium plants (an Iris, a Ranunculus, and purple loosestrife are on the list, and are marginal plants).
So, currently, there's actually NO law limiting the sale of Hygro. polysperma in Maryland. Go nuts. It will eventually likely be listed as a Tier 2 plant.
That being said, don't take it across state lines, don't mail it to someone, and above all, be responsible with this or ANY aquarium plant (or animal, be it fish or snail or shrimp or Daphnia). Don't throw it in the compost pile, dry it out before disposal. Don't flush clippings down the toilet. Don't throw in the Potomac. And above all, don't give it to Damian.
