Photo credit: © 2009 Barry Rice, CalPhotos
Report this Species!
If you believe you have found this species anywhere in Pennsylvania, please report your findings to iMapInvasives by submitting an observation record.
Species at a Glance
Waterwheel is a free-floating, rootless, aquatic plant that gets its name from its unique leaves that are whorled around the stem, resembling a wheel. It is carnivorous, behaving like a Venus flytrap and using a trap-like structure called a lamina. The lamina can snap shut in 0.01 seconds, which is the fastest recorded plant movement in the world.
Leaves: Whorls consist of 4-9 leaves arranged around a free-floating stem, giving the plant a cylindrical appearance. The leaves are up to 23 mm (2.3 cm) in diameter. The clam-like traps, called lamina, are 2-3 mm (0.2-0.3 cm) long and are held by petioles at the end of the leaves. The lamina appears as two lobes of translucent tissue that is studded inside with 4-6 bristles. The bristles protect the trap from being triggered by non-food items like floating debris. Trap lobes contain 30-40 trigger hairs which, when stimulated, cause the trap to snap shut.
Flowers: Tiny flowers with five green sepals and five white petals bloom in the summer. They are only open for 2-3 hours, usually during high sun, after which they are brought beneath the water for seed production.
Fruits/Seeds: Flowering is sporadic and not very successful, yielding only 1-10 seeds per fruit. In the fall, the plant forms turions that sink to the bottom and over-winter.
Stems/Roots: Simple or sparsely-branched stems are filled with air to aid in flotation. Stem length varies between 6 cm (2.5 in) and 20 cm (8 in).
Waterwheel may be confused with other carnivorous plants like species of bladderworts (Utricularia spp.), as well as Hydrilla (Hydrilla verticillata), naiads (Najas spp.) and watermilfoils (Myriophyllum spp.) However, waterwheel is the only plant with the distinguishing clam-like lamina.
Found in wetlands, streams and lake littoral zones, water wheel prefers clean, shallow, warm standing water with bright light, low nutrient levels, and a slightly acidic pH. Under ideal conditions it is capable of extremely rapid growth; however, it does not tolerate degraded habitats or large fluctuations in water chemistry.
Waterwheel spreads mainly through the movement of stem fragments and turions that can be transported by recreational equipment like boats and fishing gear, as well as by waterfowl that can move them between habitats. This plant is also available for sale through the aquarium and water garden industry, and can be accidentally or intentionally released.
Native to Europe, Africa, Asia, and Australia, waterwheel has only about 50 confirmed populations worldwide. Therefore, it is considered rare, but remains on the watch list because it may become threatening to native communities. In 2012, a new population of waterwheel was discovered in New Jersey, and other populations have been reported from New York and Virginia.
Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.
Due to its carnivorous nature, competition with other native carnivorous species like bladderworts is likely. Studies are needed to determine impacts on aquatic invertebrate communities and to the food web.
Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).