Big floating bladderwort (Utricularia inflata) also known as swollen bladderwort is a member of a fascinating group of freely floating, rootless, carnivorous aquatic plants. It is native to the southeastern United States, where some states list it as endangered. The PLANTS database shows that Washington is the only western state where big floating bladderwort has been introduced. Where present, in western Washington lakes, it forms dense beds of floating plants and lake residents consider the plant a nuisance.
The big floating bladderwort infestation in Washington appears to be limited to western Washington. As of 2008, Ecology botanists report big floating bladderwort from 17 western Washington water bodies, mostly in Mason, Kitsap, and Thurston Counties. We do not know who originally introduced this species to Washington, but its interesting spoke-like flowering structure and showy yellow flowers, may have made it attractive as water garden plant or aquarium plant. It is also popular with people who cultivate carnivorous plants. People have observed big floating bladderwort in isolated ponds where it is unlikely that boats visit. This leads us to speculate that species might be spreading by waterfowl.
Big floating bladderwort is an impressive freely floating plant that obtains its nutrients from the water and from tiny creatures that it captures in its seed-like bladders. These bladders are actually traps that use a vacuum to capture small invertebrates that trigger a trap door. Once inside the bladder, the plant secretes enzymes to digest the prey, providing the plant with nutrients
In Washington, big floating bladderwort flowers from June to July. When in flower, the plant forms a very distinctive wheel-like floating platform that supports a yellow snapdragon-like flower. These flowers extend about six inches above the water surface. Washington's native bladderworts do not have this floating wheel to support their flowers, but when not in flower Washington’s native bladderworts (we have several native species and some rare species) and big floating bladderwort are similar in appearance.
Big floating bladderwort reproduces from small fragments and from seed. A Florida botanist reports that when plants become stranded on mud, they can produce long threadlike branches with each bearing a tiny tuber at its tip. When not in flower, swollen bladderwort floats below the water's surface.
Photograph of Utricularia © by Kerry Dressler
There are no concerted efforts by lake residents to manage big floating bladderwort in Washington. Its dense growth habit apparently doesn’t interfere with recreational use as much as weeds such as Eurasian watermilfoil or Brazilian elodea. A fluridone treatment in Lake Limerick, Mason County, appeared to control this species for about two years and some bladderwort species are susceptible to herbicides. Grass carp will consume big floating bladderwort, although it did not appear to be a preferred species in Silver Lake, Cowliz County, Washington. Lake Limerick residents have their lake manager or sometimes students hand pull bladderworts from the lake.
Washington is also home to several native bladderwort species and people can readily distinguish all bladderwort species from other aquatic plants by the small, round, seed-like structures (bladders) that are interspersed throughout the green foliage. However, when not flowering, identifying native bladderwort plants from big floating bladderwort is very difficult
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