The genus Cabomba, which contains seven species, belongs to the family Cabombaceae, the water lily family. More commonly called fanworts, Cabomba plants are fresh water, submerged aquatic perennials that prefer a still water habitat. The plants are dimorphic, meaning that each plant has two different forms of leaves; fanworts have submerged ferny leaves and lily pad-like leaves above water. They are native to parts of South America and a few regions of North America, but people have introduced them to waterways in other countries. In some regions, it is an invasive species.
An interesting feature of Cabomba plants is the dimorphic leaves. Below the surface, the feathery leaves are multi-branched stems bearing opposite, whorled small leaves. C. caroliniana has dark green leaves that are about 3 inches (about 8 cm) long and divided into five narrow leaflets. Most of the fanwort leaves above the surface are peltate — circular with a stalk attached within the circumference of the lower surface. The purple fanwort, or C. pulcherrima, sports has deep purplish-red stems, though many of the Cabomba species have reddish stems.
Fanwort flowers are usually white or pink and rise slightly above the water level. Most are 0.5 inch to 0.75 inch (about 1.3 to 1.8 cm) in diameter, though some species have flowers that are over 1 inch (over 2.5 cm). They grow singly from the tip of the stem and most have six distinct petals surrounding a yellow center.
It is easy to miss seeing the fruit of the plant; it lies just below the water’s surface. Each plant’s fruit consists of usually three swollen carpels, which are the ovary split into many single-celled units. The fruit matures into oblong or ovoid seeds that have a cap on the narrower end. The seeds generally are about 0.3 inch by 1 inch (1 by 3 cm).
Many people use Cabomba plants as aquarium plants, but often the small leaves and stems that break away from the plant clog the pump filters. In some areas, the plant is invasive. It upsets the ecosystem, impacts water quality, and creates mosquito breeding areas by blocking moving water and generating stagnate water. The plant also impedes water distribution systems, such as dams and water intake valves. Sometimes it is so thick that it interferes with water recreation, such as boating, fishing, and swimming.
Some botanists believe that Cabomba plants were introduced to Australia’s waterways in 1967. In 1999, Australian botanists placed it on the continent’s top 20 worst weeds list — the Weed of National Significance list. In areas where the plants are invasive, water sport enthusiasts usually need to inspect their fishing equipment, including bait containers, boats and trailers, and other water sport vehicles and equipment before leaving the waterway to help prevent its spread.