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Hydrilla verticillata (L.f.) Royle
Family Hydrocharitaceae
Common name: Hydrilla, Water Thyme, Florida Elodea

Hydrilla verticillata (L.f.) Royle APNI*

Synonyms: Elodea verticillata (L.f.) F.Muell. APNI*
Hydrilla dentata Casp. APNI*
Seripicula verticillata L.f. APNI*
Udora australis F.Muell. APNI*

Description: Attached, branched submerged aquatic perennial with stems to 2 (-8) m long, usually forming a canopy immediately below the water surface; internodes to 5 cm apart in deeper water, much closer together near the surface, but usually further apart than the length of the leaves except near the tip of the stem.

Leaves in whorls of 3–8, to 4 cm long and 5 mm wide, with finely toothed margins, undersurface sometimes with prickles along midvein.

Perianth segments 1–3 mm long. Male flower 1 per spathe, without a hypanthium, released as a ripe globose bud from the spathe. Female flowers mostly 1, sometimes 2 per spathe, with a slender hypanthium, 1.5–10 cm long. Male spathe subsessile, 1.5–3 mm long.

Fruit ± cylindrical, mostly 5–10 mm long, 1.5 mm diam.; seeds 2–3 mm long.

Flowering: during warmer months.

Distribution and occurrence: Widespread in a variety of freshwater habitats; regarded as a serious weed in U.S.A.
NSW subdivisions: NC, CC, NWS, CWS, SWS, SWP, SFWP
Other Australian states: Qld Vic. W.A. S.A. N.T.
AVH map***

A native species that is not normally weedy, but may become problematic when nutrient levels rise and it may grow extremely rapidly and form dense tangled floating masses. See also Weeds in Australia profile compiled by P.G. Kodela (2008).

Text by S. W. L. Jacobs; revised by P.G. Kodela (July 2012)
Taxon concept: Flora of NSW 4 (1993)

APNI* Provides a link to the Australian Plant Name Index (hosted by the Australian National Botanic Gardens) for comprehensive bibliographic data
***The AVH map option provides a detailed interactive Australia wide distribution map drawn from collections held by all major Australian herbaria participating in the Australian Virtual Herbarium project.
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