Fanwort (Cabomba caroliniana)

Description

Fanwort, C. caroliniana, is a submersed aquatic plant with decorative leaves and attractive, emergent flowers. It can withstand a wide range of habitats, but flourishes in slightly acidic, low calcium concentration waters like those of the Adirondacks. Fanworts name is derived from its foliage's appearance, and thus its green to sometimes reddish, submersed vegetation has fan shaped leaves. The oppositely arranged leaves are usually 1-3.5cm by 1.5-6cm with 5-7 main blades that are palmately divided. Also C. caroliniana can display dark green, floating leaves that are 1-4mm by 5-30mm, alternatively arranged, and oval in shape. Fanwort displays small (1.75cm) white /cream, occasionally pink/purplish colored, solitary flowers blooming throughout the summer. 

Fanwort is considered a perennial and grows to the water surface at the beginning of the growing season (April). Soon after, it quickly occupies the water column, and the floating leaves and flowers then emerged around late June or early July. Later in the season when biomass is the greatest the plant begins to form turion like appendages at its shoot tips. Around October the stems become brittle, begin to fragment, and take on a prostrate habit on the sediments. At this time the turions either remain attached or break free while fragments form adventitious roots. In regions as north as Canada these turion like buds and stem fragments can remain green and overwinter under ice. Immediately following ice breakup in the spring, healthy rooted plants and green stem fragments are already present, and these then give rise to the next season's vegetative growth.

Native Range and Distribution

Cabomba caroliniana is considered native to southeastern United States, southern Brazil, Paraguay, Uruguay, and northeastern Argentina. Since all other species of the genus Cabomba are only found in Central and South America, it is thought that C. caroliniana is originally native to South America and has been naturalized in the southeastern United States for hundreds of years. Records of fanwort's pre-settlement distribution have not extended northward of Virginia, but since the 1930s its attractive foliage and flowers have facilitated its primary, long distance spread through the aquarium trade in the northeastern United States, Washington, and Oregon. After being first collected in New York in the Hudson Basin in 1955, its local dispersal within the state and other parts of southern New England has been attributed to boats, trailers and other aquatic equipment carrying fragments to surrounding water bodies. Recently, Fanwort has naturalized in its northern distribution and is commonly found in the Catskills and Long Island of New York. It has already been identified in the Adirondacks in Saratoga and Franklin Counties which has created a concern for its spread further into the Park.

Threats and Impacts

Fanwort is considered an invasive species outside of its indigenous regions and can cause disruption to aquatic environments and economies. Most of fanwort's negative impacts are due to its dense foliage. When the plant bed's cover exceeds 40%, fish density can be reduced which has caused commercial fishing camps to close as a result of fanworts infestation. Additionally recreational activities can be greatly hindered while real estate values have been diminished by fanwort's noxious characteristics. The competitive, vegetative growth also reduces light for benthic organisms and native plants. As a result, monocultures of C. caroliniana can form with more than 200 plants/m2; a reduction in aquatic macrophyte species richness can occur with native species displacement; and increases in epiphytic algae and macroinvertebrate abundances have been documented. Furthermore, when die back takes place in autumn alterations in nutrient cycling and depleted dissolved oxygen in water can follow.

Management

As a result of fanworts negative environmental and economic impacts, management has been implemented. The modeling of propagule pressures to identify areas most vulnerable to fanwort's invasion is important for monitoring and resource allocation. Once this invasive species becomes established its management comes at high fiscal and ecological costs. Some management practices include:

• Chemical treatment - Utilizing Fluridone and endothal (estimated to cost $200-600/ha)

• Mechanical and manual harvesting - Plants do not root deeply and are easily uprooted but viable fragments can remain in waterway

• Benthic barriers - Effective, low cost options for small scale management