Fanwort (Cabomba caroliniana) is a beautiful looking aquarium plant with fan-shaped underwater leaves. It is native to the southeastern United States, but is considered to be very weedy even where it is native. It is not native to the western United States, but has been introduced into Washington waters. Fanwort is growing in a slough off the Columbia River in the Longview/Kelso area in southwestern Washington and is also found in some coastal lakes in Oregon.
Fanwort grows very densely where it has been introduced and because it has tightly-spaced leaves, it has a tubular appearance in the water. Fanwort has been in Cullaby Lake, on the north coast of Oregon, for at least twenty years where it creates severe nuisance conditions. Fanwort is a serious aquatic weed as far north as upstate New York and Michigan (out of its native range). It clearly has the ability to grow and create serious weed problems in Washington.
Like many problem aquatic plants, fanwort can reproduce from small fragments. Fanwort stems become brittle in late summer, which causes the plant to break apart, facilitating its distribution and invasion of new waterbodies. Although fanwort produces seeds, there is no information about seed viability in the Pacific Northwest.
There has been little research on fanwort biology or management. There are reports that fanwort is less sensitive to the herbicides available for management in Washington, than other aquatic plants. Grass carp are known to eat fanwort. Unlike most other rooted aquatic plants, fanwort may get most of its important nutrients from the water rather than the sediment. Therefore, fanwort may be sensitive to reduction of nutrients in the water.
With its fan-shaped leaves, fanwort is relatively easy to identify, although there are a couple of native look-alike plants in Washington (the aquatic buttercup and the aquatic marigold) that also have fan-shaped leaves.
The fanwort infestation in Washington remains confined to a single site in southwestern Washington. Prompt action and vigilant monitoring of our lakes, may prevent further spread and increased management costs in the future. Fanwort is no longer allowed for sale as an aquarium plant in Washington, never-the-less, people must never discard the contents of an aquarium into any waters.
The line drawing of fanwort is the copyright property of the University of Florida Center for Aquatic Plants (Gainsville). Used with permission.
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