Hydrilla Hydrilla verticillata (Linnaeus f.) CasparyNon-native  -  Invasive


Hydrilla is one of the most invasive aquatic plant species in Maryland. It is found throughout the Potomac watershed all the way out to Deep Creek Lake in Garrett County, in many of the piedmont rivers like the Gunpowder and lower Susquehanna and on the Eastern Shore it has been found in the Nanticoke River drainage. Hydrilla is believed to be native to eastern Asia and Australia and was introduced into the United States in 1950's for use in the aquarium trade. Hydrilla has since spread throughout the eastern United States and waterways in the southwest and California. Hydrilla forms dense mats in waterways and limits the amount of sunlight that can reach native species thus altering the oxygen levels can result in the death of both native plants and animals. There are two forms of Hydrilla that have become established in the United States; a dioecious type, meaning the plant has only female flowers and a monoecious type which means that the plant has both male and female flowers. The monoecious type is thought to have originated from the Korean Peninsula and was first found in the United States in the late 1970's in both the Delaware River and the Potomac River. Maryland's populations are thought to be mainly of the monoecious type.


From the Invasive Plant Atlas of the United States website: Hydrilla verticillata is a submersed, rooted aquatic plant that can grow in water up to depths of 20 ft. (6.1 m). Plants can survive in depths up to 40 ft. (12 m) in non-turbid water. Leaves are whorled in bunches of 3-8, but most often with whorls of 5. The midribs of the leaves are reddish in color with the undersides having small, raised teeth. Leaves are 0.2-0.8 in. (5-20 mm) long, less than 0.1 in. (2 mm) wide and have serrated margins.

Where to find:

Look for Hydrilla in many of Maryland's waterways. The plant is especially common in the Potomac River.

There are 17 records in the project database.

View species at Maryland Plant Atlas

Hydrilla growing in the Potomac River in Allegany Co., Maryland (9/27/2014). Photo by Jim Brighton. (MBP list)

Hydrilla in Allegany Co., Maryland (10/2/2014). Verified by John D. Hall. Photo by Kimberly Booth. (MBP list)

Hydrilla pulled from the water and photographed in Anne Arundel Co., Maryland (8/22/2013). Photo by Jim Stasz. (MBP list)

Hydrilla in Lake Elkhorn, Howard Co., Maryland (7/10/2012). Photo by Jon Corcoran. (MBP list)

Hydrilla in Prince Georges Co., Maryland (7/30/2013). Verified by John D. Hall, Norton-Brown Herbarium. Photo by Bill Harms. (MBP list)

Hydrilla in Cecil Co., Maryland (9/30/2016). Photo by John Hall. (MBP list)

Hydrilla in Prince George's Co., Maryland (9/25/2016). Determined by John Hall. Photo by Bill Hubick. (MBP list)

Hydrilla in Anne Arundel Co., Maryland (8/16/2015). Photo by Kerry Wixted. (MBP list)

A comparison of Hydrilla (left) and Eurasian Watermilfoil (right) - Howard Co., Maryland (7/10/2012). Photo by Jon Corcoran. (MBP list)

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