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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”.