H. verticillata is a submerged, monoecious or dioecious perennial. Its stems are branched, about 1 mm thick and up to 3 m long;the internodes are 3 to 50 mm long. The sessile leaves are formed in whorls at the nodes;there are 3-8, sometimes up to 12 leaves in a whorl. The leaves are 7-40 mm long, linear to lanceolate, with a conspicuous midrib. They have sharply toothed margins and spines on the vein on the lower side of the leaves;a few teeth may also be formed on this vein. These leaf characteristics are commonly used to distinguish H. verticillata from similar submerged plants in the Hydrocharitaceae, like Egeria and Elodea spp.
The inflorescences are unisexual, arising from spathes situated in the leaf axils, each flower has three sepals and three petals. All six perianth parts are clear or translucent green (the sepals usually slightly reddish).The male spathe is about 1.5 mm long, solitary in the leaf axils, somewhat spiny. The female spathe is about 5 mm long, solitary in the leaf axils. There are three petals, three stamens and three styles. The ovary is cylindrical to narrowly conical and is enclosed in the base of a hypanthium;the style is as long as the hypanthium and there are three stigmas. For further information, see Cook et al. (1974) and Aston (1977).
The fruit is cylindrical, about 7 mm long and 1.5 mm wide. It contains 2-7 oblong-elliptic seeds. For further information, see Cook and Lüönd (1982);Swarbrick et al. (1981);and Yeo et al. (1984).
Related invasive species
- Hydrilla verticillata
Related Farm Practice
- Hosts
H. verticillata is a submerged fast-growing aquatic herb. It has a highly effective survival strategy that makes it one of the most troublesome aquatic weeds of water bodies in the world. It has the potential to alter fishery populations, cause shifts in zooplankton communities and affect water chemistry. It forms dense masses, outcompeting native plants and interfering with many uses of waterways. It is readily dispersed by movement of plant fragments and can produce up to 6,000 tubers per m 2. Tubers can remain viable for several days out of water or for over 4 years in undisturbed sediment. They are not impacted by most management activities, and a small percentage can sprout throughout the year making the species very difficult to manage or eradicate. It can be spread by water flow, waterfowl and recreational activities and is sold as an aquarium plant. Currently, this species is considered as one of the most aggressive invasive species in aquatic habitats. In the USA it has been listed as a Federal Noxious Weed since 1976, and is regarded as one of the worst invasive aquatic weed problems in Florida and much of the country. Its import is prohibited in Western Australia and Tasmania, and it is on the EPPO alert list.
H. verticillata occurs in lowland irrigated and tidal ricefields in South-East Asia where it is most troublesome during the first half of the growth period of the crop.