(S.G Gmel) Kuntze (Yellow floating heart )
Limnanthemum peltatum S.G. Gmel.,
Habit: Floating aquatic forb/herb
Description: Yellow floating heart is a freshwater floating perennial with stolons (runners) that aggressively root in the substrate. Most of the leaves are floating, although some remain submersed. Floating leaves range in size from 1.2 – 5.9 inches in diameter (3 – 15 cm), have slightly wavy margins, and usually grow in an opposite and unequal arrangement. The floating leaves are cordate to sub-round with rounded leaf bases (i.e., somewhat heart shaped) and are often purplish underneath. Stems are stout and branching, growing up to 0.1 inch (2 – 3 mm) thick. Flowers are yellow with five petals, each of which has fringed edges, and range in size from 1 – 1.5 inches (3 – 4 cm) in diameter. Flowers are held above the water surface on a peduncle (stalk) that can support multiple (2 – 5) flowers. Seeds are flat and oval, with winged margins that facilitate floating and attachment to animals, and are contained in beaked capsules that are 0.5 – 1 inch (1 – 2.5 cm) long.
History: Yellow floating heart was intentionally introduced in the U.S. as an ornamental plant in water gardens and escaped captivity. This species is still widely available from online sellers, despite being highly invasive, and is believed to be likely to spread as a hitchhiker on other ornamental species as well. This species is also introduced to new locations when fragments are transported on boats and its seeds can be spread by wildlife.
Biology & Spread: Yellow floating heart reproduces primarily by producing daughter plants that break off and float to new areas. This species can also spread via rhizomes and tubers. Fragments, rhizomes, and tubers are frequently spread by boats and their anchors, resulting in new introductions. Yellow floating heart also reproduces by seeds, which are spread by water currents and readily attach to feathers or fur, likely enabling the spread of seeds by waterfowl and semi-aquatic mammals as well (e.g., nutria, beaver).
Ecological Threat: Yellow floating heart grows rapidly, covering the entire surface of the water and shading out and outcompeting native vegetation. Decomposing vegetation impacts water quality and other aquatic species and shading can cause severe declines in algae, disrupting the entire food web.
US Habitat: Slow-moving, still, shallow bodies of water including ponds, lakes, reservoirs, swamps, rivers, and canals, usually at depths of 5 feet (1.5 m) or less. Unlike other species in this genus, which are all tropical/subtropical plants, yellow floating heart occurs in moderately cold temperate areas and has been found in a number of northern states in the U.S. However, this species is restricted to well-buffered, alkaline lakes with sufficient calcium for producing its floating leaves (maximum likelihood of occurrence at 188ppm CaCO3) and grows best in mineral soils (e.g., clay).
Resembles/Alternatives: Yellow floating heart resembles native big floating heart a.k.a. banana lily (Nymphoides aquatica), but can be distinguished by its yellow flowers; native Nymphoides have white flowers. Yellow floating heart also slightly resembles water lilies (genus Nymphaea), but has rounded leaf bases unlike the water lilies which have angled leaf bases (i.e., pointed tips adjacent to leaf notch). Other alternatives include little floating heart (Nymphoides cordata; native to the U.S. but not TX, not invasive), native spatterdock a.k.a. cow lily (Nuphar lutea ssp. Advena), and American white water lily (Nymphaea odorata).
Management: Prevention is the best management practice—clean, drain and dry boats, trailers, and equipment to prevent spreading this species. Physical and mechanical control methods are largely ineffective and counterproductive, as mechanical methods serve to spread fragments to new areas and the roots and rhizomes are able to survive and resprout. Raking or cutting can be used to temporarily clear areas for boater access, but repeated cutting each season will likely be required. There are no known biological controls for this species. Chemical treatment using glyphosate is somewhat effective when applied to the leaf surface with an adjuvant, but control is short-lived and repeat application is necessary. Although dichlobenil (2,6-dichlorobenzonitrile) has proven effective for controlling yellow floating heart, this chemical is harmful to fish and its use in public waters must be approved by Texas Parks and Wildlife Department as part of an aquatic vegetation treatment proposal.
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Last Updated: 2015-03-14 by JDB