Appearance Egeria densa is a submersed aquatic plant that invades freshwater systems throughout much of the United States. Often confused with hydrilla, Egeria densa has a smooth midrib on the underside of the leaf, whereas hydrilla has small teeth. Foliage The finely serrated leaves are usually less than 1 in. (2.5 cm) long and occur in whorls of 3-6. Flowers The flowers, which bloom above the surface of the water, are white with three petals. Fruit Outside of its native habitat, Egeria densa only reproduces vegetatively. Special double nodal regions can produce lateral buds, branches, and roots. Only a double node can produce a new plant when it breaks off from the parent plant. Ecological Threat Egeria densa invades both still and flowing water ecosystems including lakes, ponds, ditches, and rivers. It can form dense stands that crowd out native vegetation and reduce the area's value as fish habitat. It can also interfere with recreational activities such as fishing and swimming. This plant was first introduced into the United States in the late 1800s as an aquarium plant.