According to the Federal Noxious Weed Regulations:
(a) No person may move a Federal noxious weed into or through the United States, or interstate, unless:While the realisation that I may well be harbouring a "noxious weed" was a bit of a shock, the real issue appears to be one of transporting the plant, and potentially releasing it into the wild. According to the University of Florida Center for Aquatic and Invasive Plants, H. polysperma is present in parts of southern Texas and most of Florida, and has been reported from Virginia.
(1) He or she obtains a permit for such movement in accordance with paragraphs (b) through (e) of this section; and
(2) The movement is consistent with the specific conditions contained in the permit.
(b) The Deputy Administrator will issue a written permit for the movement of a noxious weed into or through the United States, or interstate, if application is made for such movement and if the Deputy Administrator determines that such movement, under conditions specified in the permit, would not involve a danger of dissemination of the noxious weed in the United States, or interstate; otherwise such a permit will not be issued.
(c) All such permits issued shall contain in written form in the permit any conditions (other than those conditions specified in this part) under which the permit is to be granted, e.g. conditions with respect to shipment, storage, and destruction.
(d) If the permit is denied, the applicant shall be furnished the reasons therefor.
(e) The Deputy Administrator may revoke any outstanding permit issued under this section, and may deny future permit applications, if the Deputy Administrator determines that the issuee has failed to comply with any provision of the Act or this section, including conditions of any permit issued. Upon request, any permit holder will be afforded an opportunity for a hearing with respect to the merits or validity of any such revocation involving his or her permit.
It's really a shame. The fact sheet describes almost the perfect plant for most aquarists:
Stems brittle, easily fragmenting, easily developing new stands from rooted nodes of even small fragments (Les and Wunderlin 1981). Able to form dense monocultural stands with emersed stem tips from depths as great as 3 m (10 ft) or more (Hall and Vandiver 1990). Able to photosynthesize in lower light than most native submersed species (Spencer and Bowes 1984). Tends to grow more vigorously in flowing water (Van Dijk et al. 1986). Flowers in fall and winter, with a high percentage of seed set in Florida populations (Les and Wunderlin 1981).It makes sense though. A plant that does everything an aquarist could hope for will, necessarily be a weedy species with pest potential. I need to make sure all plant bits I dispose of are dead. I generally do that anyway, not because I am conscientious but rather, because I tend to leave trimmings sit in a container for a few days before I dispose of them. In that time they dry out thoroughly. Now though, I need to make a bad habit into a rule.
Update: According to this discussion, possession in Oklahoma may be a crime. Sadly, I think it's time to get rid of all of it. Now to figure out how to do that safely.