Alligatorweed is an emergent or rooted floating perennial invasive that often forms very dense stands along the shore. The stems growing in the water are hollow and can be single or branched. Its leaves are opposite and non-succulent, elliptical or lance-shaped, up to 3/4 inch wide and 5 inches long with a prominent midrib. Soft, whitish hairs are found in the leaf axis. The white flowers occur in short, headlike spikes. The flowers resemble those of white clover. A single seed develops within the fruit.
Close-up of flower.
Infestation.