The exact number of species in the genus is unclear. Hydrilla has long stems with branch freely. Leaf midveins are often red, however, green midveins are not uncommon. Hydrilla usually feels rough to the touch. Flowers are small, about 0.16 inch across, with 3 white petals, bisexual and appear in sets of 3's.
Hydrilla often floats at the surface where it forms dense mats.
It can survive under a variety of conditions including shade, brackish water, and in either still or flowing water. Hydrilla grows so rapidly that it crowds or shades more desirable aquatic plants. Hydrilla is easily confused with Elodea spp. Both Elodea spp. It is somtimes listed as L. muscoides var.