Cabomba is an aquatic plant genus, one of two belonging to the family Cabombaceae. It has divided submerged leaves in the shape of a fan (hence the vernacular name fanwort) and is much favoured by aquarists as an ornamental and oxygenating plant for fish tanks. One species, Cabomba caroliniana, is a nationally declared weed in Australia, where it has choked up waterways after escaping from aquaria.

Taxonomy

It was published by Jean Baptiste Christophore Fusée Aublet in 1775. The type species is Cabomba aquatica Aubl.

Species

The genus Cabomba Aubl. consists of six species:

Flowers and reproduction

The perianth of Cabomba is either trimerous (having members in each whorl in groups of three) or dimerous (in groups of two) with white, oval-shaped petals, and is usually about 2.0 cm across when fully developed. The petals are unlike the sepals in that the former have two yellow ear-shaped nectaries at the base. Petals may also have purplish edges. Flowers are protogynous, having primarily female sexual structures on the first day of appearance and then switching to male on the second and subsequent days. Flowers emerge and are designed to be pollinated above the waterline. Principal pollinators are flies and other small flying insects.

Putative hybridisation

It has been speculated, that Cabomba haynesii may be a result of a putative hybridisation event involving Cabomba palaeformis and Cabomba furcata.

Cabomba as an aquarium plant

Cabomba species are popular aquarium plants. Cabomba caroliniana is easily cultivated and is tolerant of various substrates and temperatures. However, in dimly lit conditions the leaves grow small and the internodes of the stems elongate. By contrast, Cabomba furcata is considered to be difficult to cultivate in the aquarium, as it requires soft, acid water and a high light intensity.

Invasive species

Use in the aquarium trade has led to some species being introduced to other parts of the world, such as Australia, where Cabomba caroliniana it is a nationally declared weed. Having arrived in 1967, it spread rapidly in waterways and out-competed native plants, threatening water supplies, especially along the eastern side of the continent. In Australia, the cabomba weevil (Hydrotimetes natans) is introduced to waterways as a means of biological control of Cabomba caroliniana. They consume the plant's tips and inflict significant harm when present in large quantities. Larvae burrow within the stems and result in substantial damage to the main stem due to tissue necrosis. Likewise, Cabomba furcata has become an invasive species in Kerala, India, in the Kalutara district of Sri Lanka, in Chini Lake, Malaysia, and Taiwan. Its presence leads to a decline of water quality and biodiversity.