Invasive plants in general are species that were introduced to an area that is outside of their natural range of dispersal, and once introduced, will begin to grow and thrive in these new areas. Once established, these plants tend to dominate the area, selecting out native species, and in some cases destroy the overall ecosystem by eliminating all native plants and making the area useless to the animal life that once called these areas home. Invasive plants are typically characterized as adaptable and aggressive, with a very high reproductive rate. Their aggressive nature when combined with a general lack of natural enemies or predators often leads to major outbreaks that can dominate quickly and be very hard to control.
Invasive aquatic plants are plants that have been introduced into the United States and any given area from other parts of the world that have adapted to growing in, around, or near water. These plants typically fit into three categories, as they are either submerged, emergent, or floating.
Submerged or submersed plants are those plants that grow almost entirely under the surface of the water, although they do have the potential to “top out” and reach the surface. When this occurs, you may also see the tips of the plants grow long enough that they lay over and float on the surface of the water. Submersed plants typically cause the most problems for boating, fishing, and aquatic life, because of the density of their growth, and their ability to completely and quickly dominate any aquatic system in which they are found.
Emergent Plants are those species that are rooted in shallow water, but that stand upright with the majority of their plant tissue showing above the surface of the water. Typically these species will only grow in very shallow water or along the edges of the water and slightly up onto dry land. Although their growth pattern limits them to these areas, which is not typically and issue in larger lakes or ponds with deeper water, they can completely dominate shallow shoreline areas, and even worse, destroy hundreds or thousands of acres of wetlands and marsh areas which remain shallow or only slightly wet throughout the year.
Floating plants are those plants that are vascular and do have roots, but their roots are not necessarily established in the bottom sediment. These species, whether rooted or not, have most if not all of their leaves and other plant tissue floating on the surface of the water. Floating plants that are not rooted in the bottom sediment such as Water Hyacinth, Water Lettuce, and Giant Salvinia tend to be very prolific invaders as they are able to move rapidly and spread quickly over the surface of a lake or pond, and even drift or wash into surrounding water ways.
Federal Aquatic Invasive Species List: http://www.invasivespeciesinfo.gov/aquatics/main.shtml#aqpl
Federal and State Noxious Weed Lists: http://plants.usda.gov/java/noxiousDriver#state