Hydrilla verticullata, more commonly known simply as hydrilla, is an aquatic plant. It is a perennial that grows in lakes, ponds, slow-moving rivers and other bodies of water. Originally, hydrilla was probably brought into the United States as an aquarium plant. It has since been introduced into the wild and has become a problem in many areas because of its invasive and aggressive growth characteristics.
Hydrilla grows as a slender, branched plant under water. The long, slender branches are covered with small, green, strap-like leaves with serrated edges around 1 to 2 inches long. The leaves grow in whorls around the stem. The flowers are tiny and white and form on long stems. The plant is rooted to the bottom by an underground tuber attached to roots.
The plant grows as long stems that can be 25 feet long. Hydrilla forms large mats of vegetation at the surface of the water. It grows very quickly and can displace other native plants. In warmer areas, the plant can overwinter as a perennial. In colder regions, the plant dies back and regrows each year. Hydrilla can fill in a pond or small lake with vegetation.
Hydrilla is found in many bodies of waters and can handle a wide range of water quaility conditions. It can grow in water only a few inches to up to 40 feet deep. It can handle low-nutrient conditions easily and grows well in low light. Hydrilla can handle saline conditions up to 7 percent salinity.
Hydrilla is very aggressive and overgrowth of the plant can force out native plants. It also slows the flow of water in irrigation ditches, flood control canals, culverts and pumping stations. It inhibits both commercial and recreational boating and can make swimming and fishing difficult. Hydrilla can also alter the chemistry and oxygen levels in the waters it inhabits.
Temporarily draining the water from lakes or ponds can control hydrilla growth by allowing the exposed plants to die and decompose. Grass carp, an introduced species from Asia, feed heavily on hydrilla and are used to control heavy infestations in lakes and ponds. Harvesting can also help reduce vegetation, but mechanical harvesting may make things worse by breaking up the plant, seeding it again. Aquatic herbicides are also employed to temporarily control the growth.