Hydrilla verticillata: Biology and Ecology By: Carey Minteer - University of Arkansas

Background Native of southeast Asia Introduced into the United States in 1955 Federal noxious weed Since 1983 Hydrilla has been the most abundant submerged plant in Florida (McCann et al, 1996)

More Background Plants can be monoecious or dioecious (Van Driesche, 2002) Populations in the southeastern United States are dioecious and entirely female. Plants spread through vegetative regeneration. Monoecious strain found in Potomac river (Steward et al., 1984).

Monoecious strain Spreading down the Potomac river. Sexual reproduction can occur. Pollination occurs on the water’s surface Pollen is released from free floating male flowers and “caught” by the free floating female flowers (Cronk and Fennessy,2001).

Vegetative reproduction Subterranean tubers Axillary turions Fragments

Subterranean Tubers Sometimes buried several centimeters below the surface. Can sprout new shoots even after a period of 4 years. In Florida canal there are an average of 918 turions per m -2 (Sutton, 1996). Tim Murphy, University of Georgia, Bugwood.org

Axillary Turions Turions form in the leaf axils at the ends of the stems. Turions abscise and fall into the sediment. Over winter and produce new growth in the spring.

Fragmentation Spread from lake to lake by boats. Large populations found adjacent to boat ramps. Spreads extremely fast Total lake coverage can change drastically in just a years time. Raghavan Charudattan, University of Florida, Bugwood.org

Biology Monocot Family: Hydrocharitaceae Rooted submerged perennial Leaves 5-15 mm long and 2-4 mm wide Leaves arranged in pairs on lower nodes. Leaves in whorls of 3-10 on the upper nodes.

More Biology… Stems vary in length from a few centimeters to several meters. Three types: erect, horizontal, or subterranean. Erect stems support branches, leaves, and flowers. Chris Evans, River to River CWMA, Bugwood.org

Habitat Sunny Sandy substrate Low levels of rock Grows in depths between 0.7m and 2.4m Has been shown to grow in depths of up to 15m. Raghavan Charudattan, University of Florida, Bugwood.org

Habit Apical growth Several erect stems form at a single node of a horizontal stem Branches form a canopy 70% of biomass concentrated at the water’s surface (Cronk and Fennessey, 2001). Carey Minteer, University of Arkansas

Distribution

Effects on Native Vegetation Hydrilla forms lush canopies, that shades native vegetation. Alters seed banks Allelopathic Shown to inhibit the growth of Ceratophyllum demersum (coontail) (Schmitz et al., 1993).

Effects on Animals Dense stands provide refuge for young fish. High survival rates leads to over population and stunted fish growth. Predator fish cannot forage as well. Numbers and biomass of these predatory fish decline.

Effects on Human Activities Hydrilla reduces open water feeding and spawning areas of sport fish Clog boat motors Thick mats can hinder irrigation by as much as 90% (CDFA,2000). Hydroelectric power is hindered by fragmentation of plant material Wilfredo Robles, Mississippi State University, Bugwood.org

More to come… Control of Hydrilla Biological, mechanical, chemical.

Literature Cited California Department of Food and Agriculture.2000a. `Hydrilla program , Program statement 2000 season, fiscal year 200/2001. Plant Health and pest prevention services, Integrated pest control branch, Sacramento, CA. Cronk, J. and M. Fennessy Wetland plants. Biology and Ecology. CRC Press LLC, NY. McCann, J.A,, Arkin, L.N., and Williams, J.P Nonindigenous aquatic and selected terrestrial species of Florida. Orlando, University of Florida, Center for aquatic plants website. Schmitz, D.C., Schardt, J.D., Leslie, A.J., Dray, F.A., Osborne, J.A., and Nelson, B.V The ecological impact and management history of three invasive alien aquatic plant species in Florida. Biological pollution: The control and impact of Invasive exotic species. B.N. McKnight, Ed. Pp Indianapolis, Indiana Academy of Science. Steward. K.K., Van, T.K., Carter,V., and Pieterse,A.H Hydrilla invades Washington D.C. and the Potomac. American Journal of Botany 71: Sutton, D.L Depletion of turions and tubers of Hydrilla verticillata in the North River canal, Florida. Aquatic Botany53: