Yellow floating heart is a perennial, waterlily-like plant that carpets the water surface with long-stalked heart-shaped leaves. The showy five-petaled yellow flowers occur on long stalks and rise a few inches above the water. Yellow floating heart is a native of Eurasia and the Mediterranean area and has been introduced into Washington, particularly along the Spokane River near Spokane. The photograph at the top of the page was recently taken along the Spokane River. Because of the attractive yellow flowers, this plant has been sold as an ornamental water garden plants. It was recently prohibited for sale in Washington by the Washington Department of Agriculture and was listed as a Class B noxious weed in 2001. For obvious reasons, lake residents are strongly discouraged from planting yellow floating heart in lakes or natural waterbodies. These plants appear to be aggressive growers and sometimes "hitchhiker" plants such as hydrilla can also be introduced to our lakes when nursery or mail order species are planted.
Like other floating leaved plants, yellow floating heart grows in dense patches, excluding native species and even creating stagnant areas with low oxygen levels underneath the floating mats. These mats make it difficult to fish, water ski, swim, or even paddle a canoe through. It prefers to grow in slow moving rivers, lakes, reservoirs, and ponds.
Floating water heart reproduces by water dispersed seeds and by new stolens. Broken off leaves with part of a stem will also form new plants.
We have had no direct experience controlling yellow floating heart in Washington. However yellow floating heart has a similar growth habit to the fragrant waterlily and it is expected that methods used to manage waterlilies would also be effective on yellow floating heart. Waterlilies (and yellow floating heart) can be controlled by cutting, harvesting, covering with bottom barrier materials, and aquatic herbicides. Grass carp do not eat waterlilies in Washington and it is not known if they would readily eat yellow floating heart.
Look for the following characteristics:
Bright, yellow flowers about an inch or so in diameter.
Two to five flowers from each flower stalk.
Five petals per flower with a distinctive fringe along the edges of the petals.
Petals arranged like the spokes of a wheel.
Heart-shaped floating leaves with slightly wavy margins and purplish undersides.
Don't confuse yellow floating heart with Spatterdock (also called yellow pond or cow lily) which has a yellow "ball-shaped" flower and large elephant-ear-shaped leaves. Another look-alike plant, watershield, has small floating leaves with the underside often coated in a gelatinous slime.
Watershield has inconspicuous purple flowers. There are also other ornamental species of Nymphoides sp. that are sometimes sold at aquatic plant nurseries and may be confused with yellow floating heart.