Bulletin #2522, Fanwort, Cabomba
Maine Invasive Plants
Developed by the Maine Natural Areas Program and University of Maine Cooperative Extension
Threats to Native Habitats
Fanwort is a highly competitive, densely growing, submerged aquatic plant. Upon introduction into a new water body it progressively colonizes near shore areas, where it crowds out native plants and may hinder recreational activities. In relatively shallow lakes and ponds, fanwort can colonize the entire water body. Dense infestations of fanwort can alter species relationships, affect fish habitat, and impede swimming and boating. Dense infestations can degrade aesthetic and scenic quality, directly influencing tourism and real estate values. Like many invasive aquatic plants, fanwort can reproduce from small fragments. In late summer fanwort stems become brittle, and plants tend to break apart, creating opportunities for spread. As with other invasive aquatic plants, fanwort is extremely difficult to remove once it becomes established.
Fanwort is a submerged aquatic plant that produces emergent flowers, and sometimes small floating leaves. It is a perennial, growing from short rhizomes with fibrous roots. Stems may grow up to thirty feet in length. Submerged leaves are one to two inches across, with petioles opposite on the stem. Leaves are finely dissected into thin, flat segments that give each leaf the appearance of an ornate fan—an attractive pattern that has made fanwort a popular aquarium plant. Floating leaves are smaller and are not dissected though they are sometimes split at the tip. Flowers are white, with three sepals and three petals, and are typically about a half-inch wide. Flowers are solitary, each on separate stems arising from the axils of the floating leaves.
Ponds, lakes and quiet streams.
Fanwort is native to South America and some southern areas of North America. It is not clear to what extent this species is native to northern areas of the U.S., though it is found in a number of northern states. Reportedly, it is an aggressive species in northern and southern areas of the U.S. It has been widely used in the aquarium trade for a number of years, which has probably been the source of some local infestations as well as infestations in places as far away as Australia. As of 2002, there were no recorded occurrences of this species in Maine.
Prevention and Control
The best way to control this species, or any aquatic invader, is to prevent it from being introduced in the first place. Anyone engaged in activities in Maine’s waters should be aware of the potential for the spread of invasive plants and take steps to prevent their introduction. Your actions can make a difference. Simple things you can do include inspecting boats, motors and trailers at the boat ramp before launching, and again after the boat has been hauled out. Prevent plant material from getting into bait buckets and live wells, and from getting tangled up in anchor ropes or fishing gear. Plants cleaned from boats and gear should be disposed of in a trash receptacle, or away from water on dry land.
Once established, invasive aquatic plants are extremely difficult to eradicate. Control has been attempted with water level manipulations, mechanical control and herbicides. In most cases, plants have survived attempts at control. Biological controls for invasive aquatics are still being researched and may help limit growth of some species in the future. Note that the use of herbicide in Maine waters is strictly regulated. Only licensed professionals with a permit from the Department of Environmental Protection may carry out herbicide treatments in Maine’s waters. Hand-pulling of invasive aquatic plants also requires a permit. Also note that in Maine it is illegal to possess, import, cultivate, distribute or transport Cabomba caroliniana (Department of Environmental Protection, Chapter 722—An Act to Prevent the Spread of Invasive Aquatic Plants). If you think you have found an invasive aquatic plant, contact ME DEP (1-800-452-1942), or the Maine Natural Areas Program (1-207-287-8041).
Crow, G.E. and C.B. Hellquist. Aquatic and Wetland Plants of Northeastern North America. Madison: The University of Wisconsin Press, 2000.
Gleason, H.A. and A. Cronquist. Manual of Vascular Plants of Northeastern United States and Adjacent Canada, Second Edition. New York: New York Botanical Garden, 1991.
Commonwealth of Australia and National Weeds Strategy Executive Committee. Weeds of National Significance, Cabomba (Cabomba caroliniana), Strategic Plan, 2001.
For more information or for a more extensive list of references on invasive species contact:
Department of Conservation
#93 State House Station
Augusta, ME 04333-0093
Lois Berg Stack
University of Maine Cooperative Extension
495 College Avenue
Orono, ME 04469
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