SPECIES PROFILE – HYDRILLA

Thu, February 23, 2017 | Lakes and Parks

Scientific Name:               Hydrilla verticillata
Common Name(s):         Hydrilla, Esthwaite Waterweed, Waterthyme, Indian Star-Vine

Identification:
Hydrilla, Hydrilla verticillata, is a non-native aquatic plant that is commonly mistaken for the similar native Elodea, Elodea Canadensis, and the non-native Egeria, Egeria densa.  Hydrilla can be easily distinguished from Elodea and Egeria by serrations or small spines along the middle of the underside of the leaf, which are absent in both Elodea and Egeria.  Also, the flowers of Hydrilla are much smaller (1/4 inch in diameter) than Egeria (up to 3/4inches in diameter).  Hydrilla forms dense colonies and can grow to the surface in water up to 20ft deep.  It branches profusely and extends across the surface, forming thick mats. The leaves are blade-like about 1/8 – 3/8 inch long with finely serrated margins and spines on the underside which make them feel rough.  The leaves are arranged in whorls of 4-8 around the stem.  The flowers are small with three petals 1/8 – 1/4 inch long, and are transparent with red streaks, although they are rarely seen.

Range:
Hydrilla verticillata is native to Europe, Asia, Africa, and Australia, and was brought to the United States for the aquarium industry.  Live hydrilla was shipped to Florida under the common name “Indian star-vine” to be used in aquariums.  Like many aquatic invasive species, hydrilla likely got its start by a well intentioned person dumping the contents of an aquarium in a local waterway.   The first recorded wild stand of hydrilla was documented in a Florida canal in the early 1950s.  It has a tremendous capacity to quickly expand its coverage and is now well established in the eastern and southern United States and in spotty locations in the American West.

Ecology:
Hydrilla is considered a noxious pest because it grows so rapidly, outcompeting and eliminating native species such as pondweeds and eelgrass.  It also forms surface mats that hinder fishing, recreation, navigation, and water intakes.  Hydrilla can survive in both cool and warm waters.  It has become the most serious aquatic weed problem for Florida and much of the United States.  Management strategies include herbicides and biological controls like grass carp and the Asian hydrilla leaf mining fly, Hydrellia pakistanae.

Hydrilla can reproduce by several different methods which contributes to the difficulty faced by eradication efforts.  It can reproduce by tubers, much like a potato.  These tubers can lie dormant for years making total eradication very difficult.  It also spreads via fragmentation, where parts of the plant are separated from the colony and settle in new areas to form new colonies.  Hydrilla can also reproduce from seed, but it rarely does so.

Special Notes:
Here in Bella Vista, Hydrilla is not found in any of the lakes.  It was first documented at Hot Springs Village in late summer 2016 and is in numerous Arkansas reservoirs to our south.  With infested waterways within 100 miles, diligent measures should be taken to make sure our lakes remain free of this vigorous invasive plant.  Boats and equipment should be checked for fragments of plant material especially when traveling outside of Bella Vista.  Never dump bait buckets or live wells with foreign sourced water in our lakes.  Aquarium water and any aquarium contents of any kind should never be dumped into any waterway.  Once established, eradication efforts can become very expensive, with no guarantee of success.  We appreciate everyone’s due diligence in keeping our lakes free of hydrilla.