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Invasive Species Sheet - Hydrilla

Invasive Species Identification Sheet

Hydrilla (Hydrilla verticillata (L.f.) Royle)

Alternate Latin Names: Elodea verticillata (L.f.) F. Muell.; Serpicula verticillata L.f.; Hydrilla lithuanica (Andrz. ex Besser) Dandy Alternate Common Name: Indian Star-vine; Waterthyme
- perennial (occasionally annual) water plant with leaves whorled on underwater stems
- middle and upper stem whorls have mostly 5 to 8 leaves (occasionally 3 - 12 leaves per whorl)
- leaf edges are finely toothed; teeth visible to the naked eye (look closely!)
- leaves less than 1" long (1/4" to a little over 3/4" long); narrow (about 1/8" wide)
- has both subterranean turions (�tubers�) and stem turions (described below)
- plants may be rooted (in as much as 30 feet of water) or may be floating fragments
- flowers tiny, floating; petals translucent, less than 1/4" long; male flowers detach from plant

With its narrow, whorled, leaves, Hydrilla may be confused with native Water-weeds (Elodea Michx.). Native Water-weeds typically have 3 leaves per whorl while Hydrilla typically has 5-8 leaves per whorl in its middle and upper stem. In contrast to Hydrilla�s toothed leaves, the teeth on the native Water-weed leaf margins are not visible to the naked eye.

Subterranean turions (also called �tubers�) grow in the soil beneath the water at the tips of �roots� (underground rhizomes or rooted stolons spreading over the sand or mud). The �tubers� are less than 1/2" long and resemble miniature, whitish to brown-black Jerusalem artichokes; and remain viable underground for many years. Stem turions are 1/4" long, tough, green, deciduous, bud-like shoots found along the stem. Stem turions remain viable less than a year. The native Water-weeds have dark green, leafy turions at the stem tips, but no underground �tubers�.