C. caroliniana is a highly adaptable submersed aquatic macrophyte whose attractive flowers and finely dissected leaves have lead to widespread use and trade in the aquatic industry. It also has a high natural dispersal potential (...
C. caroliniana is a highly adaptable submersed aquatic macrophyte whose attractive flowers and finely dissected leaves have lead to widespread use and trade in the aquatic industry. It also has a high natural dispersal potential (Hogsden et al., 2007) due to its ability to readily fragment and spread both actively and passively. It can reach nuisance levels even in portions of its native range. The plant is typically associated with habitats that have low diversity (Lyon and Eastman, 2006). The plant also causes decreases in the biodiversity of native aquatic plants (Zhang et al., 2003).
Cabomba caroliniana A. Gray is a member of the water-shield family, Cabombaceae, a bi-generic family containing both Cabomba and Brasenia. The genus Cabomba Aublet, Hist. Pl. Guiane was first described in 1775 and is characterized by submerged rhizomatous stems, floating peltate leaves, petiolate dissected leaves and emergent hypogynous flowers (Mackey, 1996). Multiple sources report 5 species within the genus, C. aquatica, C. caroliniana, C. furcata, C. haynesii, and palaeformis (e.g. USDA-ARS, 2008; Flora of North America, 1993). With regards to the species C. caroliniana, there are two varieties. In parts of the southeastern United States, the existence of a purple-tinted flower leads botanists to treat this population as variety C. caroliniana var. caroliniana whereas South American plants having yellow flowers are treated as variety C. caroliniana var. flavida Ørgaard (Flora of North America, 1993+). However, many synonyms exist for C. caroliniana var. caroliniana, including C. caroliniana var. pulcherrima, C. australis, and C. pulcherrima (USDA-ARS, 2008).
C. caroliniana is an herbaceous, submersed, rooted aquatic species (ISSG, 2008) that often grows in water from 0.4-1.2 m and up to 6 m deep (Yu et al., 2004; Schooler et al., 2006). The plant has both submersed and floating leaves. Submersed leaves are oppositely arranged and 1-3.5 x 1.5-5.5 cm on petioles up to 4 cm long and finely dissected, having 3-200 terminal segments. Floating leaves are blades 0.6-3 cm x 1-4 mm with margins either notched or entire at base. Flowers are from 6-15 mm in diameter, flowers are white to purplish or yellow. Petals are obtuse or notched, with 3-6 stamens, 2-4 pistils and 3 ovules. Fruits are 4-7 mm, the 1-3 seeds are 1.5-3 x 1-1.5 mm long with tubercles in 4 rows (Flora of North America, 1993). The plant is fully submerged and occasionally produces floating leaves and flowers. The plant is rooted, but can survive in a free-floating state for six to eight weeks (ISSG, 2008). The plant produces fragile rhizomes, the erect shoots are green to olive green and sometime reddish brown, and are simply upturned extensions of the horizontal rhizomes (Washington State Department of Ecology, 2008).
C. caroliniana is native to subtropical temperate areas of northeastern and southeastern America (Zhang et al., 2003). It is fairly common from Texas to Florida, Massachusetts to Kansas in the USA, and occurs in southern Brazil, Paraguay, Uruguay, and northeastern Argentina in South America (Washington State Department of Ecology, 2008). The species has two varieties with different distributions. The purple-flowered variety C. caroliniana var. caroliniana occurs in the southeastern USA, while yellow-flowered C. caroliniana var. flavida occurs in South America. Widespread trade in the aquarium industry has led to its introduction in areas outside of its native range. It is widely reported as problematic in Australia, Japan, and parts of the USA (Hogsden et al., 2007). The plant is preferentially associated with low-energy, nutrient-rich systems and is commonly found in water depths from 0.4 to 1.2 meters (Yu et al., 2004).
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
C. caroliniana was first introduced beyond its native range in the eastern USA. Though native to the southeast, it was found in Massachusetts in 1920 and subsequently spread northward to Ontario, Canada by at least 1991. It is very commonly used as an aquarium plant due to its attractive flowers and finely dissected leaves, probably contributing to its introduction and spread. People in the water garden industry grow plants in Florida, Australia and Asia for distribution and sale to Europe and other parts of the USA (ISSG, 2008). Humans are the main vectors of dispersal, probably introducing the plant by either intentional water garden plantings or through inappropriate disposal. Additionally, since the plant reproduces via fragmentation, boating activity facilitates the spread of the plant; fragments are frequently observed in lakes with heavy motorboat activity (Les and Mehrhoff, 1999).
C. caroliniana spreads largely through activities related to the aquarium trade. The species is widely available from aquarium plant distributors and has long been recommended for use in aquarium gardening. The repeated and multiple introductions observed in southern New England as evident from haphazard herbarium collections indicates that accidental or intentional release from cultivation probably explains the introduction of this species in its adventive range (Les and Mehrhoff, 1999). The plant spreads most often through vegetative means, primarily through stem fragments and rhizomes (Washington State Department of Ecology, 2008). Thus, the spread of the plant increases with boating activity; it has long, trailing stems that become wrapped around boat propellers and consequently is transported within and among water bodies (Les and Mehrhoff, 1999). Though the plant flowers from May to September in the southeastern USA, the plant self-pollinates and produces seeds that germinate, though germination is not readily reported in the field (Washington State Department of Ecology, 2008).
C. caroliniana has broad environmental requirements. It often is rooted in the mud in low-energy streams and rivers as well as in ponds, sloughs, lakes, ditches, reservoirs and ponds (Washington State Department of Ecology, 2008). It can grow in water with pH from 5.7-9.2, is highly tolerant of anaerobic conditions and can survive in high alkalinity water (USDA-NRCS, 2008) and/or water with high turbidity. Growth is highest at medium turbidities, but the plant still thrives in high-turbidity water, and moderate-to-high turbidity water facilitates the production of adventitious roots (Mackey, 1996). The plant prefers warm sub-tropical climates with temperatures from 13-27 degrees C (ISSG, 2008), although it can tolerate below freezing temperatures (Mackey, 1996). In China, the plant is particularly aggressive and problematic in nutrient-rich waters.
C. caroliniana is an aggressive plant, and in many instances has seriously impacted biodiversity. C. caroliniana has a broader niche than, and may pose a threat to, native species such as Ceratophyllum demersum, Vallisneria spp., and Utricularia spp.(Cao et al., 2006). Zhang et al. (2003) report C. caroliniana presents a significant threat to Ottelia alismoides, a once common species that is seldom seen after the introduction of C. caroliniana.
The family Cabombaceae is one of the basalmost lineages of angiosperms (Aoki et al., 2004). Randomly amplified polymorphic DNA studies show the genetic variation within the genus to be low (Xiaofeng et al., 2005). In 1991, the genus Cabomba was revised by Orgaard (1991), who recognized five species, C. aquatica, C. palaeformis, C. furcata, C. haynesii and C. caroliniana, and three varieties, C. caroliniana var. caroliniana, var. pulcherrima, and var. flavida var. nov. and also suggested a basic chromosome number of x = 13. Flora of China (2001) indicates chromosome number of C. caroliniana varyingly as 2n=26, 78 or 104.
C. caroliniana is a perennial species that produces solitary hypogenous flowers with three sepals, three petals and six stamens. The flowers are 1-2 cm across and are white, yellow, pink to purple-violet. The flowers are usually pollinated by small, nectar-seeking flies (Schneider et al., 2003). Flowers are bisexual and often self-pollinated (ISSG, 2008). However, vegetative reproduction is probably the most important means of spread. The plant produces rhizomes which can easily break into fragments. Fragments can be transported both actively and passively to new areas. A fragment can regenerate into a full plant as long as it bears at least one pair of leaves (Peconic Estuary Program, 2006).
Physiology and Phenology
The plant flowers during the summer months of May to September in the southeastern United States although the plant generally self-pollinates and field germination rates are low (ISSG, 2008). In fact, the plant doesn’t produce seed in the northern parts of its range, but multiplies clonally and spreads quickly by stem fragmentation. At the end of the growing season, the stems become defoliated, brittle and hard (Mackey, 1996). These turion-like stems produced at the end of the growing season can break free and remain green at the sediment surface and help the plant to over-winter under adverse conditions (Wilson et al., 2007). Defoliated stem fragments can remain buried in mud under ice, and will regrow starting in April (Mackey, 1996). North of Queensland in Australia, C. caroliniana flowers throughout the year, while in southern Queensland, the plant may overwinter and sexual reproduction has not been documented (Mackey, 1996). In the summer in southeastern Queensland, buoyant stems up to 6 m long can grow at 5 cm per day. In the same region in July and August, the stems lose buoyancy and fragment on the soil surface. After the winter months, these fragments will re-root and grow into new plants. In mild winters, dieback may not be observed (Mackey, 1996).
C. caroliniana is highly adaptable, and will probably be found growing in habitats along with a great many other submerged aquatic plant species. However, no close associations are reported in the literature. In fact, C. caroliniana was more commonly found in areas with significantly lower biodiversity (Lyon and Eastman, 2006). Co-dominant plants observed in C. caroliniana communities in China were Ceratophyllum demersum, Hydrilla verticillata, Vallisneria natans, Potamogeton crispus and Myriophyllum spicatum (Yu et al., 2004).
C. caroliniana grows rooted in the mud in low energy streams, rivers, pools, ponds, reservoirs, impoundments and lakes. This species is not at all drought tolerant (USDA-NRCS, 2008), and grows in water at least 0.4 m deep (Yu et al., 2004). In China, Yu et al. (2004) report finding C. caroliniana typically in waters with pH 6.19-7.51, total nitrogen 0.14-3.27 mg/L, total phosphorus 0.044-0.838 mg/L and dissolved oxygen from 1.23-7.32 mg/L. The plant prefers soft, silty substrate and grows with decreased success on harder media (ISSG, 2008).
C. caroliniana does serve as a source of food for wildlife (Mackey, 1996). In an attempt to identify a suitable biological control agent for the species, several natural enemies were discovered in South America. Of the several insects, snails, and limpet evaluated, the most promising biological agents were the stem boring weevil, Hydrotimetes natans and the aquatic moth Paracles spp. (Schooler et al., 2006). The bulk of the existing biocontrol research centers on the species H. natans, the adults of which feed on foliage and the larvae mine the stems. The larvae are divers that can live under water for hours on end by holding an air bubble around the abdominal sternites. Field and laboratory studies indicate that this species is specific to fanwort (Walsh and Mattioli, 2007). The plant has been reported to be a source of food for water fowl. The Texas river cooter, Pseudemys texana feeds preferentially on C. caroliniana.
C. caroliniana disperses mainly vegetatively by rhizomes and fragments. Passive spread of fragments and seeds by water movement allows the plant to expand its population locally. Clonal multiplication happens quickly (Wilson et al., 2007), with growth rates of up to 5 cm per day (Mackey, 1996).
In parts of its range where sexual reproduction has been recorded, seeds are probably dispersed by water birds, which allows for spread among waterbodies (Mackey, 1996). Plant fragments may also travel as hitchhikers on waterfowl or wildlife.
C. caroliniana has long been used by aquarium enthusiasts. It is one of the most popular aquarium plants available from distributors. Therefore, improper disposal of aquarium specimens probably leads to a number of accidental introductions. Long fragments can also easily be wrapped in boat motors or become entangled in boating equipment, and since the plant is highly capable of reproducing via fragmentation, boating activity has definitely facilitated population expansion. In fact, more fragments are often observed in lakes with heavy motorboat activity (Les and Mehrhoff, 1999).
Because of its value to the aquarium industry, the plant is often intentionally cultivated both in its native and adventive range, where it is harvested for sale and distribution worldwide. It is suspected that at least some of the invasive populations in Queensland, Australia were intentional introductions related to the aquarium trade (Mackey, 1996). Additionally, the same qualities that make this plant attractive as an aquarium plant may also lead people to plant it in outdoor water gardens, posing a risk for release and population expansion.
C. caroliniana is an economic asset given its heavy trade in the aquarium industry. In Australia, even despite its declared status, the plant is still traded by northern growers, although its economic value is less than AUS $10,000 annually (Mackey, 1996). The economic costs of this species can be quite substantial. Infestations increase the colour of potable water, thus increasing the cost of treatment up to AUS $50 per mega litre. Dense populations can interfere with recreational activities and matted vegetation can decrease aesthetic value, resulting in a decrease in tourist dollars. For example, commercial fishing camps in the USA have been forced to close or have had incomes severely impacted and private camp owners have closed due to heavy infestations (Mackey, 1996). Economic losses are probably less severe in Australia, where natural lakes are fewer, although decreased amenity values, health risks and safety issues still threaten significant economic impacts (Mackey, 1996).
This plant is extremely productive, and can be a nuisance even in its native range (Hanlon et al., 2000). In Queensland, C. caroliniana have been shown to negatively impact water quality. The winter dieback that occurs in harsher areas of its range can cause substantial nutrient release, especially manganese pulses. This sudden manganese release can impact the manganese cycle and impact water quality. Additionally dense stands can cause water loss through seepage and overflow, thus impacting hydrological regimes (Mackey, 1996). Compared with native macrophyte beds, light is significantly attenuated under C. caroliniana beds (Hogsden et al., 2007).
Impact on Biodiversity
The impacts of C. caroliniana on biodiversity have been widely reported in the literature. It has a different ecological niche than most other aquatic plants, thus impacting native species (Zhang et al., 2003). C. caroliniana populations are often associated with areas with decreased species diversity (Cao et al., 2006). Hogsden et al. (2007) showed that while native macrophytes could be found in C. caroliniana beds, their abundance was both low and uneven. They also found that epiphytic algae is more commonly present on C. caroliniana plants, and although the community composition of macroinvertebrates was not different from native plants, C. caroliniana plants supported higher abundances of macroinvertebrates. An additional study found that species composition and species number were greater in sites without C. caroliniana (Ding et al., 2007).
While C. caroliniana has high social value as an aquarium plant, in natural systems the plant can cause substantial nuisance to recreational users by impeding navigation, tangling fishing line and wrapping motor propellers. Thick vegetation can also decrease aesthetic value. This species can also reduce swimming access and potentially cause human health safety issues (Mackey, 1996).
C. caroliniana has been grown and distributed worldwide as part of the aquarium business. In Australia, trade of C. caroliniana is a $300,000 per year business. C. caroliniana is also used in reclamation activities, primarily to remove lead from contaminated water supplies. Lead removal by C. caroliniana was 80-90% efficient at lead concentrations of one and 10 mg/L after 12-15 days of exposure (Yaowakhan et al., 2005).
Many people value C. caroliniana for its use as an aquarium plant. Many find its flowers and feather-like foliage quite attractive. Its tolerance of a wide range of environmental conditions means it is relatively easy to grow in home aquariums.
C. caroliniana is a productive aquatic macrophyte which can cause nuisance problems. However, in highly degraded systems, it does sequester nutrients, which means it can be useful in the revegetation of impacted ecosystems. It might help to shift a waterbody away from an algal-dominated state. The plant can also provide environmental benefits typical of plants of similar ilk. Fanwort provide oxygen to the surrounding water, habitat to macroinvertebrates and fish, and is used as food by water fowl and wildlife (Mackey, 1996).
Due to the petiolate finely dissected leaves, C. caroliniana can be readily confused with Ranunculus aquatilis. Such misidentification has been reported in the literature (Les and Mehrhoff, 1999). It is also easily confused with a number of other species by those who are not practiced in the identification of aquatic plants. The leaf morphology looks similar to that of Ceratophyllum spp., Myriophyllum spp. and Megalodonta beckii, or other such species. However, C. caroliniana is differentiated from these species by its petiolate leaves and white, yellow, or purple flowers. Differentiation of the five Cabomba species is a bit more difficult, and must take into account seed size, shape and surface quality (Mackey, 1996).
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
The vegetative propagules of this species are very easy to spread. Therefore, educational programs are usually necessary to decrease human-mediated spread. Teaching users how to clean equipment in a way that decreases the chance of transmission is one way to lessen the impact of the human vector. This species has been declared noxious in several states and countries.
Because this species reproduces vegetatively quite quickly, rapid response to decrease the population spread is integral to successful management. This species has been shown to be relatively resistant to physical and chemical management techniques, therefore an integrated management plan should focus on early detection and rapid response (Wilson et al., 2007).
Numerous educational campaigns have been directed at informing the public about the danger of aquatic invasive species. Areas in which C. caroliniana is particularly problematic commonly distribute informational materials about its identity as well as how to report new invasions. Other educational campaigns have been directed toward informing the public about how to clean equipment in order to prevent the movement of invasive species.
No reports of eradication exist in the literature.
Cultural control and sanitary measures
Fragments are easily transportable, thus it is extremely important to decrease the instances of accidental introduction by addressing humans as a vector. By establishing guidelines on how to properly clean equipment, dispose of aquarium water, and identify target plants, it is likely that instances of accidental transportation and release will be fewer.
Mechanical harvesting has been used to control C. caroliniana, but since the plant spreads via fragmentation, mechanical control cannot be expected to provide any benefit beyond temporary nuisance relief. Draining and drying are viable means of physical control (Wilson, 1997). Benthic barriers, drawdown, sediment removal, rotovation and shading are additional techniques that have been used with some success (USACE-ERDC, 2008). Since fanwort needs direct sunlight for growth, shading may be a good control method for small populations or early infestation (Peconic Estruary Program, 2006). However, other authors report that the plant has been shown to be relatively resistant to mechanical management techniques (Wilson et al., 2007).
Since plants can spread via fragments, much attention has been given to decrease human-mediated dispersal. The plant has been officially listed as a noxious weed in the USA and Australia. Some states have put in place legislation to regulate the sale, transportation and introduction of C. caroliniana.
Schooler et al. (2006) state that no effective population control measures exist to control fanwort populations. Therefore, surveys to identify biological control agents have been conducted in the plant’s native range of South America. The most promising agents are the stem-boring weevil Hydrotimetes natans and an aquatic moth (Paracles spp.). The stem-boring weevils were predicted to have a larger impact on deep-water C. caroliniana populations, while the moth larva is expected to control shallow-water populations (Schooler et al., 2006). Additionally, triploid grass carp have been used as biological control agents in Florida (Hanlon et al., 2000); however, there remains some concern with incomplete sterilization and release of this non-selective grazer.
It is generally reported that C. caroliniana is resistant to chemical control techniques. C. caroliniana is sensitive to 2,4-D (Wilson, 1997). Fluridone has been shown to give good control, in all treatments tested, significant reduction of shoot dry weight was achieved; however, the rates that gave more than 80% control had undesirable effects on non-target water marigold species (Nelson et al., 2002).