Sorry, no, you have "gathered" completly wrong
If I'm wrong then explain why Hygrophila polysperma is able to be sold in this country. It's on the list. It's recognized as invasive in several states and yet, here in New York, it's sold freely. Maybe you should actually look at the APHIS web site before you judge whether or not someone is wrong.
This was pulled directly from the APHIS site regarding Hygrophila:
Noxious Weed Information:
Hygrophila polysperma (Roxb.) T. Anders.
This plant is listed by the U.S. federal government or a state. Common names are from state and federal lists. Click on a place name to get a complete noxious weed list for that location.
United States:
Miramar weed Noxious weed
Alabama:
Miramar weed Class A noxious weed
California:
Miramar weed Quarantine
Florida:
hygrophila Prohibited aquatic plant, Class 2
Massachusetts:
Miramar weed Prohibited
North Carolina:
Miramar weed Class A noxious weed
Oregon:
Miramar weed Quarantine
South Carolina:
Miramar weed Invasive aquatic plant
Indian hygrophila, Miramar weed Plant pest
Vermont:
East Indian hygrophila Class A noxious
You'll notice that these are the only states that currently have the plant on their noxious weed lists. Not all of them have prohibited the plant. It depends on the state.
New York State, interestingly enough, has no noxious weed list.
Further, this might be of some use to you:
The Plant Protection Act (Title IV of the federal Agriculture
Risk Protection Act of 2000) replaces 10 existing federal
laws with one statutory framework. This new act provides the
USDA with the ability to prohibit or restrict imports, exports or
interstate movements of noxious weeds.
Subtitle A of the Plant Protection Act:
Section 412: The USDA may prohibit or restrict the
importation, entry, exportation, or movement in interstate
commerce of any plant, plant product, biological control
organism, noxious weed, article or means of conveyance,
if the
USDA determines that the prohibition or restriction is
necessary to prevent the introduction into the United States or
the dissemination of a plant pest or noxious weed within the
United States.
You might also want to look at this: (Taken from
http://nationalplantboard.org/docs/usdaqua.pdf)
1. IMPORTED PLANTS AND PLANT PARTS 7 CFR 301.10 and 11
PEST: Various
STATES REGULATED: All
REGULATED ARTICLES: According to federal foreign quarantines, some plants and
plant parts may be imported into some States or areas of the United States but are
prohibited from being imported into, entered into, or distributed within other States or areas.
RESTRICTIONS: Whenever any imported plant or plant part is subject to such
destination restrictions (1) the State(s) or area(s) into which the plant or plant part is allowed to be imported is quarantined with respect to that plant or plant part; and (2) no person shall move any plant or plant part from any such quarantined State or area into or through any State or area not quarantined with respect to that plant or plant part.
Unless the plant is prohibited or quarantined within a state (or part of that state) there is no action taken. Further, it is not illegal to ship that plant to a state if a) your state has no quarantines regarding that plant and b) the state you're shipping it to has not prohibited that plant. So, yes, a noxious weed can be considered to be regulated by the USDA. However, what action, if any, is taken depends entirely on whether or not that plant is requlated within a given state/region.
The USDA doesn't just put blanket bans on the plant material that can be moved around the country. They work with state regulatory agencies to determine what action, if any, is needed regarding pests and weeds. The officials and ecologists within each state determine whether or not a plant is noxious
within that state.
To illustrate that point, here is an excerpt from the Florida Department of Agriculture's Plant Industry Division's policy regarding noxious weeds:
5B-57.004 Introduction, Possession or Movement of Arthropods, Biological Control Agents, Plant Pests, Noxious
Weeds, and Invasive Plants, Regulated by the Department.
(1) It is unlawful to introduce, multiply, possess, move, or release any arthropod, plant pest, biological control agent, noxious
weed, or invasive plant regulated by the department or the USDA except under permit issued by the department unless a federal
permit, PPQ 526, has been issued by the USDA with concurrence by the Department. No permit shall be issued nor concurrence
with a federal permit, PPQ 526 made unless the department has determined that the arthropod, plant pest, biological control agent,
noxious weed, or invasive plant can be contained to prevent escape into the environment or that it will not pose a threat to
agriculture, beneficial organisms, or the environment or become a public nuisance.
Again, the plant can be on the noxious list but still be distributed in the state (in this case by permit only) if it is deemed to not be a threat to the local environment or economy of Florida.
These are just some examples of how the law is treated in different states. There are many more available if you're willing to tool around on the APHIS website. But, before you go around saying that I'm wrong, do some research. Whatever you've gathered is obviously misleading at best.