Where it's from

India

What Hydrilla does to the habitat

Hydrilla grows into mats that cover the water and block out light for native species below. Since it can photosynthesize in extremely low light, it can start very deep and work its way to the surface at the rate of one inch a day, where the branches turn horizontal to cover the entire area.

Hydrilla’s chemical warfare consists of raising the pH factor in the water, lowering the oxygen and raising the temperature of the water. It also causes water to stagnate creating an ideal breeding ground for mosquitos.

It is a hindrance to navigation and recreation on the water.

Management

Small infestations can be handled with a tarp or opaque fabric secured directly over the young plants.

Means of mechanical control include pond rakes and cutters. Be aware that these are only short term solutions and you will have to go back and repeat the process periodically.

Florida has spent millions battling Hydrilla and new gizmos have been created like a vacuuming pump managed by a diver, tillers, hydraulic arms, even rotovators.

People have even introduced grass carp (illegal in some states) to eat the invasive.

DESCRIPTION

Botanical Glossary

Hydrilla verticillata is a submerged, aquatic perennial herb that can grow from depths of 6 m (20 ft.). The plants have both a monoecious and a dioecious form. The leaves of the plants are 2-4 mm (0.07-.15 in.) wide (down to 1 mm (0.04 in.) on monoecious plants) and are 0.6-2 cm (0.2-0.8 in.) long. The leaves are whorlled around the stem, with 3-8 leaves per whorl. There can be "sharp" spines of variable size along the margins of the leaves, giving them a toothed appearance. The leaves have a midrib which is reddish in color. This plant has various methods of reproduction. The monoecious form of the plant produces female flowers that have three translucent petals that may contain a few red streaks. These flowers are 1-5 cm (0.4-2 in.) long and 4-8 mm (0.15-0.3 in.) wide. There are also three sepals that are white in color. The flowers are attached to the axils of the leaves by a long hypanthium. The male flowers also have three petals that are around 2 mm (0.07 in.) long and are colored anywhere from white to red. There are three white, red or brown sepals. These flowers are short stalked, detaching from the plant and floating to the water surface. The dioecious plants in the U.S. so far are female (however the hydrilla collected in Connecticut did not have flowers present). Another reproductive structure which makes these plants a successful invaders are the stem tubers (turions). The stem tubers are bud-like structures that are produced along the stems of the plant, and can vary in color from dark green, to grey to whitish. They are 0.6 cm (0.25 in.) long and often appear spiny. These structures can break off of the plant and survive the winter in the sediment at the bottom of waterbodies. Tubers are also another way in which these plants spread. These tubers form at the end of the rhizomes of the plant and are 5-10 mm (0.2-0.4 in.) long and white or yellow in color. Page References Crow & Hellquist 31, Flora of North America 35, Gleason & Cronquist 637, Holmgren 606.