L. peploides is a productive emergent aquatic perennial native to South and Central America, parts of the USA, and likely Australia (USDA-ARS, 1997). It was introduced in France in 1830 and has become one of the most damaging invasive plants in that country (Dandelot et al., 2008). It is often sold as an ornamental, which likely explains its introduction to Europe. It has been more recently introduced to areas beyond its native range in the USA, where it is often considered a noxious weed (INVADERS, 2009; Peconic Estuary Program, 2009). L. peploides is adaptable, and tolerates a wide variety of habitats where it can transform ecosystems both physically and chemically. It sometimes grows in nearly impenetrable mats; it can displace native flora and interfere with flood control and drainage systems, clog waterways and impact navigation and recreation (Peconic Estuary Program, 2009). The plant also has allelopathic activity that can lead to dissolved oxygen crashes, the accumulation of sulphide and phosphate, ‘dystrophic crises’ and intoxicated ecosystems (Dandelot et al., 2005).
Ludwigia, the only genus in the Jussiaeeae tribe, is both very large and very diverse, with around 82 species in 23 sections (Zardini et al., 1991). L. peploides belongs to sect. Oligospermum, whose members are morphological very closely related. Four subspecies have been recorded: Ludwigia peploides subsp. glabrescens (Kuntze) Raven, Ludwigia peploides subsp. montevidensis (Sprengel) Raven, Ludwigia peploides (Kunth.) Raven subsp. peploides, and Ludwigia peploides subsp. stipulacea (Ohwi) Raven (USDA-ARS, 1997; Jiarui et al., 2007).
L. peploides is an emergent and floating herbaceous perennial macrophyte. It has glabrous or pubescent stems 1-30 dm that can creep horizontally as well as grow vertically. Early growth resembles a rosette of rounded leaves growing on the water’s surface. Alternate leaves are polymorphic and less than 10 cm long and oblong to round, often lanceolate at flowering. The species exhibits root dimorphism and has adventitious roots that form at nodes and ensure oxygen uptake. Flowers are 5-merous (pentamerous), grow from leaf axils, are bright yellow, and can be from 7 to 24 mm long. Fruit is in a five-angled reflexed capsule, about 3 cm long that contains 40-50 seeds 1.0-1.5 mm long, embedded in the inner fruit wall (EPPO, 2004; The Jepson Online Interchange, 2009).
L. peploides is native to South and Central America, parts of the USA, as well as perhaps Australia (McGregor et al., 1996; USDA-ARS, 1997). A number of sources indicate that L. peploides is ‘likely’ to be native to Australia, but there is some disagreement regarding its nativity to Australia (CEH, 2007). Recent reports of the plant from New York and Washington, USA indicate that its range may be expanding in the USA (Peconic Estuary Program, 2009; Washington State Department of Ecology, 1994-2009; The Jepson Online Interchange, 2009). L. peploides subsp. peploides and glabrescens are native to the USA, whereas the subspecies montevidensis is widely recognized as having been introduced (Estes and Thorp, 1974). L. peploides is also reported as having been introduced to Belgium, France, Italy, the Netherlands, Spain, Switzerland, the UK, Portugal and Cuba (CEH, 2007).
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.
L. peploides was introduced from the Americas to Montpellier in France in the 1830s, likely as a result of ornamental plantings. It has since become one of the most widespread and detrimental aquatic invasive plants in that country (Ruaux et al., 2009). L. peploides was recently introduced beyond its native range in King County in Washington State, USA (Washington State Department of Ecology, 1994-2009). It was first observed in New York, USA in 2003 in the Peconic River (Peconic Estuary Program, 2009).
It is most likely that escape from aquaculture explains most of the adventive introductions; this plant is very commonly sold as an ornamental. Despite its very rapid growth, and invasive nature, it is still marketed and sold as an ornamental, so the risk of introduction, whether accidental or intentional, is still high. Its ability to spread rapidly through vegetative means, coupled with a high degree of phenotypic plasticity (Ruaux et al., 2009), also means that the plant is quite likely to establish upon release. The plant is listed as a noxious weed in Washington State (USA), South Africa, and was added to the EPPO Alert List in 2004.
L. peploides can be found in wetlands, on shorelines, in slow-flowing rivers, ponds, rice fields, marshes and in other freshwater environments (USACE-ERDC, 2009). It has proven to be relatively frost-tolerant in the UK (CEH, 2007). The plant grows in water up to 3 m deep and can reach up to 80 cm above the surface of the water (EPPO, 2004); it is also tolerant of flooding (CEH, 2007).
Impacts on the local environment by L. peploides can be devastating. The species possesses an allelopathic activity that has year-long effects on water quality and can lead to impoverished flora by decreasing seedling survival of vulnerable native taxa (Dandelot et al., 2008). L. peploides can also cause severe hypoxia and sometimes anoxia during the summer. It can also lead to reduced sulphate and nitrate levels and increased sulphide and phosphate concentrations. These combined effects have the capability of fomenting what Dandelot et al. (2005) refer to as “a dystrophic crisis” and an intoxicated ecosystem. The plant has been reported to outcompete native Myriophyllum and Potamogeton species in France, which translates to a reduction in macroinvertebrate habitat (Dutartre, 1986; CEH, 2007). It also supplants native wetland grasses, some of which are used as forage for livestock (CEH, 2007).
L. peploides (including all subspecies) is a diploid species with chromosomes numbering 16 (2n). Zardini et al. (1991) report that nearly all species in sect. Oligospermum can hybridize and produce vigorous offspring. The species has demonstrated a high degree of phenotypic plasticity.
This species has a seasonal development pattern. In France, leaves appear at the surface of the water in early spring. Up to 50 cm of stem is produced by June, and flowering occurs from July to October. Aerial stems fall during November, and persistent organs fall to the sediment in a dense mat (Dandelot et al., 2008). This species reproduces primarily through clonal expansion; stem fragments are spread by animals, humans, and water currents (Ruaux et al., 2009). L. peploides is self-compatible and the species has a very high potential seed output (10,000 – 14,000 seeds per square metre) (Ruaux et al., 2009). In a study of locally collected seed material from nine populations in the middle Loire River in France, fruits had a buoyancy duration of around 2 weeks, and fruits were very frequently viable, indicating that although clonal expansion is the species’ primary means of reproduction, sexual reproduction may be an important means of survival and spread (Ruaux et al., 2009).
Physiology and Phenology
This species can grow in a broad range of habitats due to its high degree of genetic polymorphism and phenotypic plasticity (Ruaux et al., 2009). Its allelopathic properties mean it is an ecosystem engineer, and by making habitats unsuitable for native flora, it increases its competitive potential (Dandelot et al., 2008).
The water primrose beetle, Lysathia ludoviciana has been observed to selectively feed on L. peploides (Campbell and Clark, 1983). The beetle is native to the southern USA and Caribbean region; its USA distribution has been reported to include Texas, Georgia, South Carolina, Ohio and Alabama (Habeck and Wilkerson, 1980). Several species from Argentina, including Tyloderma spp., Auleutes bosqi, Onychylis sp. nr. nigrirostris and Lysathia flavipes have been reported to have L. peploides as their only host (Cordo and DeLoach, 1982); however, the use of non-native biological control agents can be a risky endeavour.
L. peploides disperses mainly through the movement of plant parts in water, and simple hydrochory can generate substantial propagule pressure. However, sexual reproduction and transportation of the resulting seeds may also be an important means of dispersal (Ruaux et al., 2009).
Stems can be carried by animals to new locations, where new populations can establish and grow via vegetative expansion (Ruaux et al., 2009). Studies quantifying the pressure due to natural vectors have not yet been conducted.
Release from ornamental plantings of L. peploides is likely primarily responsible for the introduction of the species in its adventive range. L. peploides has been historically valued as an ornamental; ornamental plantings likely explain its introduction to Europe (Ruaux et al., 2009). Although still available from online distributors, current educational efforts aim to decrease the probability that this plant will be intentionally introduced, and hopefully cut down on accidental release in areas where this plant has been declared a noxious weed. Hitchhikers are often present in horticultural plantings and can thus be included in orders of non-invasive plants. It is possible that this plant may unintentionally be introduced by people intending to cultivate a comparatively harmless plant.
L. peploides has showy bright-yellow flowers that make it an interesting candidate for aquaculture. Additionally, the plant demonstrates a high degree of phenotypic plasticity, which allows it to adapt to a broad range of growing conditions and water regimes (Ruaux et al., 2009). Unfortunately, the very characteristics that make it a hardy and amenable garden specimen, also lend it the ability to invade a broad range of habitats where it very often is invasive (Ruaux et al., 2009). This plant is still offered for sale through internet horticultural distributors, so the probability of intentional introduction is quite high. Current educational efforts aim to decrease the possibility that this plant will be intentionally introduced, and will hopefully reduce the chances of accidental release in areas where this plant has been declared a noxious weed.
L. peploides can double its biomass in 15 to 20 days in slow flowing water (EPPO, 2004), and the resulting mats can drastically reduce water flow (Dandelot et al., 2008). Along with closely related Ludwigia grandiflora, L. peploides is considered by some to cause the most damage in aquatic systems across many regions of France, blocking slow-moving waterways, and impacting irrigation and drainage in lakes, ponds and ditches (Ruaux et al,. 2009). The plant can also cause hyper-sedimentation and silting (Dandelot et al., 2008). In France, the plant can displace native wetland grasses that serve as forage for livestock (CEH, 2007). In Chile it is reported as a weed of rice (Ramírez, 1991).
This species has an allelopathic effect that impacts water quality throughout the year. When the plant is at nuisance levels, the effects on dissolved oxygen, sulphide, phosphate, and pH levels can lead to impoverished flora by decreasing seedling survival of vulnerable native taxa (Dandelot et al., 2008). Its tendency to grow in thick mats also contributes to physical alteration of the environment, making it unsuitable for sensitive species.
When invasive, this species causes declines in biodiversity (EPPO, 2004) through shading, competitive exclusion, and chemical allelopathic alteration of the growing environment. Due to the species’ allelopathic activity, it poses a severe threat to vulnerable native flora (Dandelot et al., 2005). Additionally the plant provides little in terms of suitable habitat. The dense surface matting excludes the growth of native species, shades out submersed aquatic vegetation, and is inhospitable for fish and invertebrates. As well as providing unsuitable habitat, it is also of little use as a food source; it contains saponins and calcium oxalate, which make it unpalatable to most herbivores. Where it is invasive, it often has far reaching and negative effects on multiple trophic levels (Dandelot et al., 2008).
This plant can grow very densely, impeding navigation and interfering with hunting, fishing and other recreational activities (CEH, 2007). Dense matting also provides excellent mosquito habitat, which is compounded by the tendency of the mats to exclude fish that prey on mosquito larvae.
There has been some study regarding the use of this plant in the treatment of wastewater. It is capable of producing large amounts of biomass in the presence of elevated nitrogen levels (Rejmánková, 1992). However, it may be less adept at removing dissolved phosphorus, as an Australian study reports it had negative growth in all phosphorus concentrations investigated (Wen and Recknagel, 2002). Additionally, the plant has attractive yellow flowers that make it an interesting specimen for water gardening.
Water garden enthusiasts may have an aesthetic appreciation of this species. It shows some potential for use in wastewater treatment (Rejmánková, 1992) although other studies have concluded that many other species are preferable to L. peploides in wastewater processing. Little information is available regarding other beneficial social uses of the plant.
Due to the plant’s phenotypic plasticity, it could possibly be used in the reclamation of severely impacted ecosystems. However, its tendency towards invasiveness coupled with its allelopathic potential make this plant a poor candidate for restoration projects, at least for projects outside the plant’s native range.
L. peploides is very likely to be confused with other Ludwigia species. Zardini et al. (1991) report that taxa of sect. Oligospermum are “notoriously difficult taxonomically; morphological distinctions between them are often not sharp. The entire sect. Oligospermum is a polyploid complex whose members form a very closely related group. L. peploides is especially similar to Ludwigia grandiflora and Ludwigia hexapetala. These plants can be distinguished by their flowers. L. peploides stems grow more horizontally and their petals are usually 1.0-1.5 cm long, and anthers are 1.0-1.7 mm, whereas L. grandiflora and L. hexapetala stems grow vertically and have larger petals and anthers. Additionally, the small leaves at the base of the flower are triangular to egg-shaped in L. peploides, whereas those of L. hexapetala are ovate (EPPO, 2004).
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.
L. peploides is valued as an ornamental, therefore educational programmes must be directed to educate the public about the dangers this plant poses outside its native range. Teaching users how to clean equipment in a way that decreases the chance of transmission is one way to lessen the impact of human-mediated transport. Additionally, information should be disseminated regarding the responsible propagation and cultivation of this species if it will continue to be sold as an ornamental.
It is much easier and more effective to attempt to control this plant early in its introduction timeline. Small populations are effectively controlled by hand pulling, prior to significant clonal expansion.
Numerous educational campaigns have been directed at informing the public about the danger of aquatic invasive species like L. peploides in areas where they pose a threat. Governmental organizations disseminate educational materials about the identification and control of this species, as well as the importance of preventive measures in slowing or stopping the spread of this plant. As the species is still widely available, there is an opportunity for education to happen at various points along the horticultural trade pathway from distributor to introduction.
Cultural Control and Sanitary Measures
As stem fragments are easily transportable, it is extremely important to decrease the instances of accidental introduction by addressing humans as vectors. 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 decrease.
A number of physical control measures including hand-pulling, rotovation, and mechanical harvesting may be used to control L. peploides; however, all fragments and roots must be removed to prevent re-establishment (CEH, 2007). It is likely that mechanical treatment of large populations would provide only temporary nuisance relief.
Plants can spread locally when seeds and fragments drift in water currents or are carried to new areas by animals, but most attention should be given to addressing forms of human-mediated transport. The availability of this plant as an ornamental, and its ability to spread vegetatively from small amounts of material indicate that controlling human behaviour and increasing awareness might be the most effective way to reduce introductions of L. peploides.
Sterile grass carp, Ctenopharyngodon idella, have been used to control L. peploides (Manuel, 1989). However, grass carp are non-selective herbivores that will almost certainly harm native species. Some study of native biological control measures has revealed promise in using highly specific herbivores to control the plant, although appropriate caveats regarding the introduction of a non-native control agent remain.
Control of L. peploides is difficult. The plant has been used in the past to absorb herbicide residues in runoff water (CEH, 2007). Several herbicides have been used with reported success, including halosulfuron-methyl, glyphosate and triclopyr (CEH, 2007).