N. peltata is an aquatic, bottom-rooted perennial plant with floating leaves, which can grow in dense mats and reproduce prolifically through both vegetative and sexual means. These dense mats have caused many negative environmental and eco...
N. peltata is an aquatic, bottom-rooted perennial plant with floating leaves, which can grow in dense mats and reproduce prolifically through both vegetative and sexual means. These dense mats have caused many negative environmental and economic impacts, which include displacing native species, reducing biodiversity, decreasing water quality, impeding recreational activities, and diminishing aesthetic value. N. peltata is very difficult to control due to its ability to form a new plant from rhizomes, stolons, separated leaves, or seeds. The dispersal of N. peltata to new locations may be aided by the transport of seeds by avian vectors (Cook, 1990); however, the trade and potential escape of N. peltata through the water garden industry may play a larger role in its spread (Les and Mehrhoff, 1999). N. peltata is declared a noxious weed in New Zealand and parts of North America (NWCB, 2007), and is also declared as invasive in Sweden (Gren et al., 2007). Other species of Nymphoides also have the potential to become invasive, and N. indica and N. cristata have been recorded as problematic in Florida, USA.
The genus Nymphoides (family Menyanthaceae) is generally accepted as containing 39 species (USDA-GRIN, 2004), which occur primarily in tropical and subtropical regions, though also in certain temperate regions of both the Northern and Southern hemispheres (Ornduff, 1966). The genus name comes from the Greek nympha meaning ‘nymph’ and oides meaning ‘resembling’ (IN-AIS, 2005). Nymphoides peltata was first named Menyanthes nymphoides by Linnaeus in 1753, revised to Limnanthemum peltatum in 1770 by Gmel., and further revised in 1891 to its current accept scientific name, Nymphoides peltata (S.G. Gmel.) Kuntze. N. peltata is synonymous with N. flava and N. orbiculata. Limnanthemum cordatum, described from a specimen collected in northeast Guangdong, China, and is probably also synonymous with N. peltata (Flora of China, 2002). In Europe there are possibly two races, a western European sub-oceanic and a Siberian continental race (Meusel et al., 1978). The English common names, yellow floating-heart and fringed water lily, refer to the species bright yellow flowers with distinct fringed petals, that rise above the slightly heart shaped leaves floating on top of the water’s surface.
N. peltata is an aquatic, bottom-rooted perennial plant with round, floating leaves, yellow flowers borne upon peduncles rising above the water's surface, and long branching stolons with adventitious roots beneath the water’s surface. The circular to slightly heart shaped floating leaves are 3-15 cm in diameter on long stalks that attach to underwater rhizomes. The floating leaves have slightly wavy, scalloped margins and are alternately arranged at the stem base but are opposite at the apex (Flora of China, 2002). They are a green to yellow-green colour above, and are often a purple colour on the underside of the leaf. Each peduncle that rises a few inches above the water surface can have two to five flowers, which are bright yellow, have five distinctly fringed petals, and are 3-4 cm in diameter. Both long- and short-styled flower morphs are usually needed to sexually reproduce (Ornduff, 1966). The fruit is a 1.2-2.5 cm beaked capsule that contains many flat, smooth, ovoid seeds with winged margins. The seeds are approximately 0.4 mm thick, 3.8-5.1 mm long, and 2.7–3.0 mm broad (Cook, 1990). The seeds also have winged margins which aid attachment to avian vectors and floatation (Cook, 1990).
N. peltata is native to Eurasia and the Mediterranean (NWCB, 2007), as well as China, India, and Japan (IPANE, 2003). Unlike the majority of Nymphoides spp., which mostly occur in the tropics and sub-tropics, N. peltata is the only species in the genus occurring in moderately cold temperate areas (Meusel et al., 1978). In Japan, N. peltata was once common, but is now listed as a ‘vulnerable’ species (Environment Agency of Japan, 2000), and the last population that retains both floral morphs of distyly needed for sexually reproduction is located in Lake Kasumigaura (Takagawa et al., 2006). N. peltata was introduced to North America during the late nineteenth century, and has steadily spread and been repeatedly introduced across the United States and parts of Canada. In Sweden, N. peltata was first reported as being introduced in 1870, and has been repeatedly introduced and spread to approximately 40 lakes and rivers (Larsson and Willén, 2006). N. peltata was relatively recently recorded in New Zealand in 1988 and its establishment is known from only one field site (ENVBOP, 2003). There are also reports that N. peltata has been introduced to Ireland (BioChange, 2007), although the origin of the introduced plant is stated as Brazil (FAO-UK, 2000), which was not found to be part of the native range of N. peltata during this review.
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.
N. peltata was first recorded in the United States in 1882 in Winchester, Massachusetts. There is also a report of N. peltata in New York City’s Central Park in 1886. Multiple records from Washington D.C. during the 1890s reported N. peltata in several United States Fish Commission ponds as being ‘naturalized and spreading into adjacent ponds’. Other first recordings include Missouri in 1893, Louisiana in 1899, and Pennsylvania in 1905. The earliest record of N. peltata in the Hudson River was in 1929 from New York, and its origin was speculated as being an escape from a water garden or pool (Stuckey, 1973).
The first records of N. peltata in the Midwestern United States were in Ohio in 1930, Indiana in 1945, and Illinois in 1948. In the Southwest, it was recorded in Oklahoma in 1935, and it was believed to be introduced by either being planted along with other water plants and fish being transferred into the lake, or possibly the seeds were transported in by waterfowl (Stuckey, 1973). N. peltata was also recorded in the Western U.S in 1930 in Long Lake in Washington (Ornduff, 1963). Records also exist for: Arizona, Arkansas, California, Connecticut, Kentucky, Maryland, Mississippi, New Hampshire, New Jersey, Rhode Island, Tennessee, Texas, and Vermont (USDA-NRCS, 2005). Within the last five years, N. peltata has also been recorded in Virginia, Maine, Oregon, and Nebraska (USGS-NAS, 2007).
N. peltata was first recorded as a non-native plant in Sweden in 1870, and it is known to have been intentionally introduced multiple times in the early nineteenth century (Gren et al., 2007; Hallstan 2005). A single plant released into the River Arbogaån, Sweden in 1933 had spread to cover an area of 45km² by 1975 (Löfgren, 1993). Larsson and Willén (2006), record 40 lakes and rivers containing N. peltata populations, with an overall estimated coverage of approximately 430 km² when just examining populations established in lakes (Gren et al., 2007). N. peltata has also been introduced intentionally as an ornamental, and its first record was pre-1866 (BioChange, 2007). From 1987 to 1999 it was recorded as being present in 10 hectads (1 hectad = 10km x 10km).
N. peltata is a relatively recent arrival in New Zealand, and was first recorded in 1988 (NZPCN, 2005). Its population is reported as being localized to only one known field site (ENVBOP, 2003). N. peltata is declared a noxious weed in New Zealand and parts of North America (NWCB, 2007), and is also declared as invasive in Sweden (NOBANIS, 2005) and Ireland (BioChange, 2007).
N. peltata has not spread as quickly as other aquatic invasives, but its potential invasiveness should not be overlooked (Les and Mehrhoff, 1999). N. peltata is a popular water garden plant, and the ability to order this plant over the internet and through mail order gives it the ability to travel to all parts of the world. It has escaped confinement and has been intentionally introduced on several occasions beyond its native range. In the locales where it has been introduced, it has often become the dominant plant species, outcompeting native species and displacing other species which depend on the ecosystem. N. peltata has the potential to colonize large areas within one growing season by means of vegetative propagation (Brock et al., 1983), and a single plant can produce over 100 new plants in only 12 weeks (Zhonghua et al., 2007).
N. peltata prefers slow moving rivers, lakes, reservoirs and ponds, but can also grow in damp mud, swamps and wetlands. It is also known to occur in ditches, canals, waterways, and “break-through” pools of dikes (Van der Velde, 1979). Backwaters which are influenced by high river levels and flooding in the winter are frequently habited by N. peltata (Van der Voo and Westhoff, 1961). It occurs primarily in slow-moving, eutrophic, alkaline waters at depths less than 3.0 m (Van der Velde et al., 1979).
N. peltata is a hexaploid (x = 9) having 2n=54 (Ornduff, 1970). There is a report of 2n=24 from a specimen analyzed by Wang (1940), however multiple reports from widely separate locations found 2n=54, and the report by Wang needs verification. N. peltata has 6 complete sets of chromosomes in each cell, and its nuclear DNA expressed on a diploid basis is equal to 1.4 pg/2C (BioChange, 2007). In Japan, where N. peltata is a listed as a ‘vulnerable’ species (Environment Agency of Japan, 2000), research is being conducted on possibly restoring remnant N. peltata populations by using the genetic diversity stored in the seed banks in order to reduce the genetic inbreeding of the current, low genotypic populations (Uesugi et al., 2007).
N. peltata is able to reproduce prolifically by vegetative and sexual means. It can reproduce by seeds, stolons, or broken-off leaves with part of a stem attached. Seed production usually requires cross-pollination between the long- and short-styled floral morphs, but self-pollination may result in the formation of small capsules with 10-20 seeds, a quarter of the number of seeds usually found in capsules from cross-pollinations. In addition, the seeds from self-pollinated capsules have a lower viability compared with those seeds formed from cross-pollination (Ornduff, 1966). Van der Velde and Van der Heijden (1981) noted 44 species which visited flowers during their study, 43 of which were species of Hexapoda and one species of Aranea. Species of Apidae, Syrphidae, and Ephydridae seem to be the most important in regards to pollination. The release of developed seeds occurs 32-60 days after the anthesis of the flowers (Van der Velde and Van der Heijden, 1981). Van der Velde and Van der Heijden (1981) also found an average density of 180 fruits per square metrein natural populations, and a max density of 310 fruits per square metre in experimental populations. The seeds of N. peltata are unable to germinate under hypoxic conditions, and need only a short cold period to overcome their innate dormancy (Smits et al., 1990). N. peltata seeds also show great tolerance with respect to desiccation (Smits et al., 1989).
Physiology and Phenology
N. peltata flowers from May to October in the United States (USGS-NAS, 2007), and from October to April in New Zealand (NZPCN, 2005). Each flower survives for only one day. Leaf life span lasts from 23-43 days, determined by multiple factors such as exposure to various weather elements, water fluctuations, and substrate (ISSG, 2006). N. peltata overwinters as dormant tuberous rhizomes.
N. peltata is a true freshwater species, and does not occur in areas where the average concentration of chlorine rises above approximately 300mg/L. The occurrence of N. peltata is restricted to well-buffered alkaline lakes due to the species requirement of calcium for production of floating leaves (Smits et al., 1992). Maximum probability of occurrence was found at 3.76 meq/L (Smits et al., 1988), equivalent to 188 ppm CaCO3. The northern limit of distribution corresponds approximately with the 16°C July isotherm (Van der Velde et al., 1979). N. peltata needs ample light and oxygen, and its seeds are unable to germinate under hypoxic conditions (Smits et al., 1990). N. peltata grows best on mineral bottoms such as clay (Van der Velde, 1979).
Anas platyrhynchos (mallard duck), Fulica atra (coot), and Cyprinus carpio (common carp), have been known to consume and digest the seeds of N. peltata in laboratory studies (Smits et al., 1989). Damage to the floating leaves of N. peltata caused by the caterpillars of Cataclysta lemnata in the hydrophobous stages has also been observed by Van der Velde (1979). Lammens and Van der Velde (1978) report that Lymnaea stagnalis (pulmonate snail), Deroceras laeve (slug), and the larvae of Nausinoe nymphaeata (moth) and Cricotopus trifasciatus (midge) also consume the leaves. Ondatra zibethicus (muskrat) and Fulica atra (coot) were also recorded as consuming the leaves.
Hydrochory, the dispersal of seeds by water currents, seems to be the main dispersal mode of seeds within a water body (ISSG, 2006). The flat, slightly hydrophobic seeds are often seen floating on the water surface in chain-like rafts, loosely connected by the marginal bristles on each individual seed (Cook, 1990).
Vector Transmission (Biotic)
N. peltata seeds have been shown to be completely digested by Anas platyrhynchos (mallard duck), Fulica atra (coot), and Cyprinus carpio (common carp), adding evidence that endozoochory, the transport of seeds within an animal, will not contribute to successful dispersals between water bodies. However, epizoochory, the transport of seeds externally on animals, has been suggested as a possible dispersal mechanism for movement between isolated water bodies (Smits et al., 1989; Cook, 1990). The unique seed structure of N. peltata contains marginal trichomes that readily attach to the feathers and fur of certain waterfowl and mammals. Cook (1990) reported that the flanks, the region between bill and eyes, the webs of the feet, as well as the bill and shield could transport N. peltata seeds in waterfowl such as A.platyrhynchos and F. atra. Cook (1990) notes that seeds could also potentially be transported by some amphibious mammals.
N. peltata has been introduced accidently through flooding of ornamental ponds into surrounding natural waterways. It is also possible for N. peltata to be a ‘hitchhiker’ plant with other species ordered through water garden catalogues.
N. peltata has been repeatedly intentionally planted as an ornamental in different water bodies throughout Sweden and the United States since its first introduction in the late nineteenth century (Josefsson and Andersson, 2001; Stuckey, 1973). The trade of this plant as an ornamental through the internet and mail order has greatly increased its availability and ease of spread into new environments.
Control efforts in Sweden involving the mechanical cutting and removal of N. peltata are estimated at costing 28,000 SEK (4,500 USD; 3,000 EUR) per hectare, or 56,000 SEK (9,000 USD; 6,000 EUR) annually if the recommended procedure of cutting twice a year is followed (Gren et al., 2007). The loss of recreational and aesthetic value associated with N. peltata can also cause a decline in lakefront property values (DCR, 2004) as well as possible declines in tourism-related income for the community.
N. peltata alters the chemical composition of the water body by increasing the organic content and contributing to internal fertilization by taking up nutrients from the sediment during growth and releasing them back into the water column during decomposition (Josefsson and Andersson, 2001). Where introduced, N. peltata can be an excellent competitor for light, and has been known to out-compete native aquatic vegetation and phytoplankton. Dense mats of N. peltata also lower the amount of oxygen in the water (NatureServe, 2008).
Impact on Biodiversity
N. peltata reduces biodiversity by competing with and displacing native vegetation, and is capable of changing the fauna and flora of an ecosystem during periods of mass occurrence (Josefsson and Andersson, 2001). N. peltata has been shown to exert a strong interspecific interferential effect on the floating leaved species Trapa bispinosa (Zhonghua et al., 2007) and Larson (2007a) has shown that one-sided competition from N. peltata has a profound effect on the submerged aquatic plant community due to its ability to outcompete submerged vegetation for light.
N. peltata can form dense mats that impede recreational activities such as boating, fishing, swimming, water skiing, canoeing, and kayaking. In addition, unsightly mats of vegetation decrease aesthetic values, and alter the ecosystem in which they occur. These declines in recreational and aesthetic values can decrease tourism, which can be a major source of income within the community.
Species in the genus Nymphoides look very similar to those in the genus Nymphaea (water lilies), but Nymphoides have rounded, not angled leaf bases and produce much smaller flowers that are borne above the water surface on stalks. There are many other Nymphoides species that look very similar to N. peltata, and flowers are essential to identify the various species in the genus. N. cordata and N. aquatica arenative in the United States, while N. indica and N. cristata are non-native and have been introduced in several locations throughout Florida (USGS, 2002).
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.
Several publications have been produced in the United States regarding the impacts of aquatic invasive species such as N. peltata, and the steps that lake recreationists need to take in order to prevent introducing and spreading aquatic invasives.
New Zealand aims to eradicate N. peltata from all known sites within 10 years (NWCB, 2007).
Cultural control and sanitary measures
Several regions in the United States require that recreationists drain all water and clean off all gear (boats, trailers, fishing equipment, etc.) used on water bodies in order to minimize the chance of spreading invasive plants, such as N. peltata, to other areas.
Attempts to control N. peltata have been very difficult due to its ability to propagate vegetatively through fragments, and through underwater roots and rhizomes. Attempts to mechanically harvest only serve as a means of creating and introducing more plant fragments, and potentially aiding in dispersal to new locations. The leaf petioles are cut by mechanical harvesting, but will eventually form new leaves, requiring one or two cuts each spring and summer to maintain controlled areas (CAPM-CEH, 2004). Both roots and rhizomes are also able to withstand mechanical removal by dredging (Josefsson and Andersson, 2001), and it is too expensive to be considered solely as a method of weed control (CAPM-CEH, 2004). The current cost to mechanically cut and remove N. peltata and its fragments is estimated at 28,000 SEK (4,500 USD; 3,000 EUR) per hectare, and since it is recommend to be repeated twice a year, an annual cost of 56,000 SEK (9,000 USD; 6,000 EUR) per hectare (Gren et al., 2007).
Hand raking can be effective in very small, localized areas where fishing or navigation lanes need to be created (CAPM-CEH, 2004). It may also be possible to alter water depth and flow speeds in channels to make them inhabitable, or cover small areas with opaque floating material (CAPM-CEH, 2004).
Dichlobenil (Midstream GSR, Casoron G, Luxan dichlobenil) has been effective in controlling N. peltata (CAPM-CEH, 2004). A granular treatment is applied in the spring when growth is just beginning, but before the leaves reach the water's surface. In order to assure the chemical is applied evenly over the treated area, motorized or hand operated applicators are recommended. The chemical manufacturers do not recommend treating more than 20% of the water body at one time, nor do they recommend use in waters where flow is greater than 90 m/hour. A combination of mechanical removal of floating leaves mid-summer with subsequent application of dichlobenil has worked in rapid control situations.
Glyphosate has also been used to control N. peltata, but it is less effective than dichlobenil and does not give reliable control. Trial studies show that spraying floating leaves between July and September show 40-50% control lasting for one season, while other trials showed recovery towards the end of the season and no long-term control (CAPM-CEH, 2004). In New Zealand, spraying glyphosate or Penetrant has been reported as effective, though repeated applications may be necessary (ENVBOP, 2003).
NOBANIS, 2005. NOBANIS - invasive alien species fact sheet - Nymphoides peltata. In: Online Database of the North European and Baltic Network on Invasive Alien Species - NOBANIS, NOBANIS. http://www.nobanis.org