Common Name: Marsh Pennywort
Scientific Name: Hydrocotyle umbellata
Order: Arecales
Family: Apiaceae
Wetland Plant Status: Obligatory
Ecology & Description Marsh pennywort is an herbaceous perennial. It is green in color and requires full sun. Marsh pennywort can be floating, with stems protruding into the water. It can be easily pulled from water, and is a common method for removal of large quantities. Stems (petioles) are approximately ¼” in diameter, up to 12” long, attaching at the center of the leaf. Roots form at the nodes. Leaves are centered on the stems, round to kidney-shaped, and notched or scalloped at the margins. The color is green to bright green, ½” to 3” wide. Veins extend out from the point of attachment to the stem. Marsh pennywort can have from 5 to 10 very small star-shaped flowers per stem. Color can be light green, yellowish green, white, or purple. Fruit and seeds are rarely occurring, usually between 1 March and August. Paired nutlets are slightly flattened, /16” long.
Habitat Marsh pennywort occurs in moist or shallow water. The stem can be extending above water with the leaf fully exposed, where soil can provide root support. It can be found along pond edges in moist soil, in shallow areas of ponds, and mud flats. The plant can form mats in shallow water, impeding water flow and reducing oxygen for aquatic life.
Distribution Northeastern United States - Connecticut, Indiana, Massachusetts, Michigan, New Jersey, New York, Ohio, Pennsylvania, Rhode Island Northwestern United States - Oregon Southeastern United States - Alabama, Arkansas, Delaware, Florida, Georgia, Louisiana, Maryland, Mississippi, North Carolina, South Carolina, Tennessee, Virginia South-Central United States - Texas Southwestern United States - California
Native/Invasive Status Marsh pennywort is native to lower 48 states of the United States, but it is an invasive species.
Wildlife Uses Marsh pennywort does not have any nutritional value as a wildlife food. It is considered an aquatic or terrestrial noxious weed. It can shade water surfaces and reduce water temperature, and provide minimal cover for waterfowl. By shading moist areas, it can maintain moisture for various organisms. It has been used for various human diseases, illnesses, and deficiencies, but in small continual doses. No scientific research has been documented to confirm the potential for remedies. It can cause nausea and other intestinal issues in humans.
Management & Control Techniques Marsh pennywort, commonly known to yard maintainers as dollarweed, can be controlled through cultural practices, chemical application, and mechanical removal. Cultural practices may include mowing grass to a level that will provide mulch to control various weeds. Mowing grass to control moisture to minimal but adequate levels can also reduce occurrence. Irrigation must also be monitored, and can be changed at the appearance of pennywort to reduce moisture or frequency of added moisture. The plant is re-establishing. Chemical application can be employed to kill the plant. Herbicides should be chosen as selective as to not impact desirables. Herbicide is most effective when weeds are young. Careful planning and decision-making should be considered for aquatic applications. Pre-emerge herbicide can be utilized to control before appearance. Mechanical removal may be necessary when pennywort has produced mats in aquatic beds. Additionally, hand-pulling can follow as part of an effective monitoring plan. Landscaped beds may also require hand-pulling or herbicide treatment.
References Kelly, A. 2006. Removal of invasive floating pennywort Hydrocotyle Ranunculoides from Gillingham. Conservation Evidence 3:52-53. Davenport, M. 2008. Dollarweed. Clemson Cooperative Extension, Clemson, South Carolina.
This document was authored by Rodney McKay, School of Forestry, Louisiana Tech University, March 2015.