Alternanthera is a genus of approximately 80 herbaceous plant species in Amaranthaceae, the amaranth family. It is a widespread genus with a cosmopolitan distribution.
Several species are aquatic plant in habit, but most are spreading stoloniferous plants, sometimes used as ground cover. The leaves are simple and verticillate. The small white or yellow flowers are arranged in chafflike bracts, growing in the leaf buds.
Alligator weed (Alternanthera philoxeroides), a native of South America, forms dense, sprawling mats, reaching 15 m across. It is considered a noxious weed, choking ponds, lakes, streams, canals, and irrigation ditches.
It is being suppressed through biological control with the alligator weed flea beetle (Agasicles hygrophila), the alligator weed thrips (Amynothrips andersoni), and the alligator weed stem borer (Vogtia malloi). Mechanical and chemical controls fail.
There are only a few aquatic plants in the genus Alternanthera suitable for aquarium use. They are considered difficult to grow and maintain, because they are sensitive to certain parameters of light, water, and fertilizers. The species often found in aquarium settings include A. bettzichiana, A. reineckii, A. reineckii var. lilacina, A. reineckii var. roseafolia, A. reineckii var. rubra, and A. sessilis, which is semi-aquatic.