Scientific Name: Alternanthera philoxeroides
A native of South America, alligatorweed was inadvertently introduced to Southeastern U.S. in the late 1800s. Its white flowers are clover-like and bloom a summer.
Most commonly found floating in mats along the water’s edge, alligatorweed also grows immersed and even terrestrially. Its opposing leaves are lance shaped, 1-2 inches long, and have a distinct midrib. When it grows aquatically, its stems grow hollow for buoyancy.
Damage — Alligatorweed infestations cause several problems. Flooding and erosion; the floating mats can get caught up around dams and other structures, such as fallen trees and bottlenecks. It has been known to grow across waterways to become a hazard to navigation. Infestations dampen aesthetic value, inhibit recreational activities such as boating, swimming, and fishing, and harbor mosquitoes.
Spread – So far, alligatorweed has been spotted in 12 states and Puerto Rico, spreading mainly by fragmentation. Boaters should beware when moving their trailers and watercraft from waters with alligatorweed present to insure they do not inadvertently spread this invasive.
Control – In North Carolina, herbicides are the primary method of control. It’s tough to manage – even annual herbicide sprayings can fail to control it. Two varieties of insects have been employed as biological control agents — the flea beetle and a stem borer moth. Neither are particularly effective in WNC.