October 2011
Murdannia is Murder
Murdannia keisak (Hassk.) Hand.-Maz
Contact: Wesley M. Knapp, Maryland Department of Natural Resources
WKnapp@dnr.state.md.us
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Photographs courtesy of B. Eugene Wafford, University of Tennessee, Knoxville
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ANNAPOLIS, MD (October 20, 2011) - Murdannia keisak, or marsh dayflower as it is sometimes called, is a beautiful wetland plant native to Asia, bearing small but showy purple-white flowers. Don’t let this plant’s beauty mask its true nature. It is a horribly invasive species establishing itself along our streams, choking our native vegetation, and becoming more and more established in Maryland every year. Marsh dayflower is just finishing flowering and starting to set seed. The time to stop it is now and that’s why the Maryland Invasive Species Council has named it our October Invader of the Month.
Marsh dayflower is a fairly distinctive species. It has stems that are fleshy and root at the nodes. The stems grow flat (prostrate) along the ground and eventually ascend upward to a height of up to 20 inches. The leaves are alternately arranged, lance-like in outline, up to 3 inches long and less than 1/3 inch wide. The flowers occur at the ends of the stem or in the axils (where the leaves join the stem). The flowers have three pink to purple/white petals, and are found individually or in small clusters of two to four in September and into October. The fruits are capsules that produce small seeds about less than 1/8 inch in length. Marsh dayflower’s spread is also aided by its ability to vegetatively reproduce, meaning that plant fragments left behind after incomplete removal can regrow.
Marsh dayflower is a member of the Spiderwort family, a family with deep horticultural roots. You may be familiar with the many different types of beautiful Spiderworts planted in gardens or found natively across the State. Marsh dayflower’s history in North America, however, has nothing to do with ornamental horticulture. It is believed that the marsh dayflower was accidently introduced in the United States from Asia in 1935 during a failed attempt to grow cultivated rice in the U.S. Since this initial introduction it has spread in the Southeast. It was first reported in Maryland in 1971 from the Eastern Shore. Since then it has become well established in the coastal portions of the state. Recent reports place this plant as far west as Montgomery County. In the southeast where the marsh dayflower has a longer history of establishment it has spread well beyond coastal areas and is found frequently in the mountains. In some states, such as South Carolina, it is found in almost every county. It should be expected to spread into every county in Maryland given enough time.
Marsh dayflower can be found in freshwater marshes, edges of ponds, ditches, shallow freshwater wetlands, and streams. It is not an overly large plant, being just 12-30 inches long but the stems lie flat against the ground. This forms a mat of vegetation that prevents other species from growing. At one site in coastal Delaware just a few miles from the Maryland line, marsh dayflower has become so abundant it is now the dominant plant. This dominance has left little physical habitat for native plants and is believed to be the reason for the decline of many rare plant species located in these wetlands.
Control of marsh dayflower is a task that has proven to be very problematic, yet will be increasingly necessary to keep this species from becoming common and widespread in Maryland. Marsh dayflower is an annual plant which means it has to be controlled for many years to deplete the quickly abundant seed source. Hand pulling, getting all the roots, can be effective if done before the plant sets seed. Currently few herbicides are known to control this species. Treatments of glyphosate have been shown to be ineffective when applied early in the season. Mechanical control should be avoided because it readily reproduces from vegetative fragments. Because it is found in wetlands, the number of herbicides available for controlling the marsh dayflower is limited. Contact your local or state forestry office or University of MD Cooperative Extension office for specific recommendation and as always follow label directions.
For more information, please visit:
Invasive Alien Plant Species of Virginia
For more information about Invasive Species of Concern in Maryland, visit www.mdinvasives.org