Summary of Invasiveness
Azolla filiculoides is a small fern native to the Americas which has spread widely throughout the world by a variety of mechanisms, of which man has become the most significant (Lumpkin and Plucknett, 1982). Man has introduced A. filiculoides into Europe, North and sub-Saharan Africa, China, Japan, New Zealand, Australia, the Caribbean and Hawaii.
In eutrophic water systems, A. filiculoides grows rapidly, easily outcompeting indigenous vegetation. Decaying root and leaf matter below a mat of A. filiculoides, coupled with the lack of light penetration, creates an anaerobic environment which can reduce the quality of drinking water and make survival for other organisms in the water impossible.
Preferred Scientific Name
Azolla filiculoides Lamarck
Preferred Common Name
Other Scientific Names
These are considered to be junior synonyms of Azolla filiculoides
Azolla bonariensis Bertoloni
Azolla japonica Franch. & Sav.
Azolla magellanica Willd.
Azolla squamosa Molina
International Common Names
English: fairy moss; mosquito fern; Pacific azolla; red water fern; water fern; water velvet
Spanish: helecho acuatico; hlechito del aqua; lenteja de agua
French: fougere d’eau
Local Common Names
China: xi lu-ping; xi man jiang hong
Germany: grosser algenfarn
Netherlands: grote Kroosvaren
South Africa: rooivaring
According to Lumpkin and Plucknett (1980), A. filiculoides is native to the Rocky Mountain states of the western USA and Canada, through Central America and to most of South America. It has been introduced to Europe, North and sub-Saharan Africa, China, Japan, New Zealand, Australia, the Caribbean and Hawaii.
Distribution Table and Maps
The distribution in the summary table and maps below is based on all the information available, as given in the ISC.
|India||Present||Parimal & Kushari, 2002|
|-West Bengal||Present||Parimal & Kushari, 2002|
|Iran||Present||Native||Invasive||Khoshravesh et al., 2009|
|Israel||Present, few occurrences||EPPO, 2014|
|Japan||Present||Introduced||Seto & Nasu, 1975|
|Egypt||Present||Magda et al., 2002; EPPO, 2014|
|South Africa||Widespread||Introduced||Invasive||Twyman & Ashton, 1972; Twyman & Ashton, 1972|
|Zimbabwe||Present||Chikwenhere, 2001; Chikwenhere, 2001|
|-British Columbia||Present||Native||USDA-ARS, 2003|
|-Alabama||Present||Native||Richerson & Grigarick, 1967|
|-Arizona||Present||Native||Richerson & Grigarick, 1967|
|-California||Present||Native||Richerson & Grigarick, 1967|
|-Florida||Present||Native||Madeira et al., 2013|
|-Louisiana||Present||Native||Richerson & Grigarick, 1967|
|-Mississippi||Present||Native||Richerson & Grigarick, 1967|
|-Texas||Present||Native||Invasive||Richerson & Grigarick, 1967|
|CENTRAL AMERICA AND CARIBBEAN|
|Costa Rica||Present||Native||USDA-ARS, 2003|
|Trinidad and Tobago||Present||Introduced||Reed, 1965|
|-Rio Grande do Sul||Present||Native||Reed, 1962|
|-Sao Paulo||Present||Native||Tofoli et al., 2000|
|French Guiana||Present||Native||Svenson, 1944|
|Belgium||Present||Introduced||Lawalree, 1964; EPPO, 2014|
|Bulgaria||Present||Introduced||Sourek, 1958; EPPO, 2014|
|Czech Republic||Present||EPPO, 2014|
|Czechoslovakia (former)||Present||Introduced||Sourek, 1958|
|France||Present||Introduced||Chevalier, 1926; EPPO, 2014|
|Germany||Present||Introduced||Schloemer, 1953; EPPO, 2014|
|Greece||Present||Introduced||Royal Botanic Garden Edinburgh, 2003;EPPO, 2014|
|Hungary||Present||EPPO, 2014; Royal Botanic Garden Edinburgh, 2003|
|Ireland||Present||Introduced||Brunker, 1949; EPPO, 2014|
|Italy||Present||Introduced||Royal Botanic Garden Edinburgh, 2003;EPPO, 2014|
|Netherlands||Present||Introduced||Sculthorpe, 1967; EPPO, 2014|
|Poland||Present, few occurrences||EPPO, 2014|
|Portugal||Present||Introduced||Invasive||Reed, 1962; EPPO, 2014|
|Romania||Present||Introduced||Lawalree, 1964; EPPO, 2014|
|Russian Federation||Present||EPPO, 2014|
|-Central Russia||Present||EPPO, 2014|
|Spain||Present||Introduced||Royal Botanic Garden Edinburgh, 2003;EPPO, 2014|
|UK||Present||Introduced||Invasive||Royal Botanic Garden Edinburgh, 2003;EPPO, 2014|
|-Victoria||Present||Introduced||Allinson et al., 2000|
|New Zealand||Present||Introduced||Bailey, 1902; Large & Braggins, 1993|
History of Introduction and Spread
A. filiculoides, the type species of the genus, is widely distributed, having been introduced to a number of countries in which it is not indigenous (Ashton, 1982). The plant has been dispersed by a variety of mechanisms, of which man has become the most significant (Lumpkin and Plucknett, 1982).
According to Szczesniak et al. (2009), A. filiculoides was first recorded in Europe towards the end of the 19th century, and the first observations were made in 1870s-1880s. The species may have been accidentally transported in ballast tanks of ships, in water with fry, or directly as an ornamental. Janes (1998a) noted the deliberate introduction of the plant as an ornamental into Europe through mainland Britain at the end of the 19th century. Possibly as a result of its various transport routes, A. filiculoides appeared independently in different places at almost the same time. It then spread across nearly all of Europe.
A. filiculoides was introduced into Asia from East Germany in 1977 as an alternative to the cold susceptible native strain of A. pinnata, used as a green manure in the rice industry (Lumpkin and Plucknett, 1982). It was introduced to Africa in 1948 as an aquarium plant (Oosthuizen and Walters, 1961; Jacot-Guillarmod, 1979).
A. filiculoides has also been spread around the world as a model plant for the study of Azolla-Anabaena symbiosis (Carrapiço, 2010) Risk of Introduction
Further spread is likely as A. filiculoides continues to be sold in nurseries as a fish pond plant. In Africa and Europe, dispersal between countries will no doubt continue due to the movement of waterfowl, which can spread plant fragments between bodies of water. A. filiculoides will continue to invade countries where the presence of eutrophic waters, lack of natural enemies and an unregulated nursery trade will contribute to its status as a weed. Hosts/Species Affected
A. filiculoides is not generally considered a weed of crops. It is commonly grown in conjunction with rice, asA. filiculoides has the ability to fix nitrogen via an endosymbiotic blue-green alga (Wagner, 1997), acting as a green manure in rice cultivation. However, in its introduced range,A. filiculoides may impact upon trout and other fish farming (McConnachie et al., 2003). It has also been recorded to affect the growth of Potamogeton crispus L. (Janes et al., 1996).
Notes on Natural Enemies
Host records from around the globe show that the genus Azolla is attacked by generalist herbivores and that very few specialist insect species have evolved on these plants (Hill, 1997). However, four beetle species, the weevils Stenopelmus rufinasus and S. brunneus and the two flea beetles Pseudolampsis guttata and P. darwinii, appear to have specialised on the genus Azolla (Richerson and Grigarick, 1967; Habeck, 1979; Hill, 1999) and were identified as potential biological control agents for A. filiculoides in South Africa (Hill, 1997). Following host range testing,Stenopelmus rufinasus was released in 1997 as a biocontrol of A. filiculoides in South Africa (McConnachie et al., 2004).
Means of Movement and Dispersal
The economic impact of A. filiculoides in South Africa was examined by McConnachie et al. (2003). Thick mats on reservoirs and slow-moving water bodies caused economic losses to water-users. Among those water-uses most seriously affected were farming (71%), recreational (24%), and municipal (5%). On average, A. filiculoides was found to cause on-site damages of US$589 per hectare per year.
In eutrophic water systems, A. filiculoides grows rapidly, easily outcompeting indigenous vegetation. Decaying root and leaf matter below a mat of A. filiculoides, and the lack of light penetration, creates an anaerobic environment. Not only can very little survive under such conditions, but the quality of drinking water is reduced, caused by bad odours, colour and turbidity (Hill, 1997). Cases have been reported where both livestock and game farmers have lost animals due to them refusing to drink from infested water bodies or drowning as a result of mistaking the mat for solid ground. The weed also reportedly increases water loss through evapotranspiration and promotes the development of waterborne, water-based and water-related diseases (Hill, 1997).
A. filiculoides infestations may form thick mats (5-20 cm thick), on water bodies up to 10 hectares in size (McConnachie et al., 2003). Such infestations have been shown to severely impact the biodiversity of aquatic ecosystems and have serious implications for all aspects of water utilization (Gratwicke and Marshall, 2001).
One of the last remaining habitats of the endangered fish species, the eastern Cape rocky (Sandelia bainsii Castelnau, 1861; Anabantidae) in South Africa, had become so overgrown with the weed that had the biological control programme not been so successful, S. bainsii faced extinction.
South Africa is the only country that has initiated a classical biological control programme against A. filiculoides. Four insect species were identified as potential biological candidates – all frond-feeding beetles: Pseudolampsis guttata (Leconte) (Chrysomelidae), P. darwinii (Sherer),Stenopelmus rufinasus Gyllenhal and S. brunneus Hustache (Curculionidae). All species do extensive damage to the plants in the country of origin (Hill, 1997).
The biology and host range of P. guttata was investigated by Hill (2002), and although it was found to be fairly damaging, the weevil S. rufinasus was identified as the most suitable of the four for release in South Africa, and was imported into quarantine for host-specificity screening. The weevil was released in 1997 and results have been dramatic, causing local extinction of A. filiculoides at the sites where it was released (McConnachie et al., 2004).
The surface area of weed controlled totalled 203.5 ha and infested sites were controlled in approximately seven months on average (in a range of 3-11 months). Five years after the release of the weevil, A. filiculoides no longer poses a threat to aquatic ecosystems in South Africa and its effects on the utilization of water resources have been significantly reduced (McConnachie et al., 2003). S. rufinasus has been released in Mozambique and Zimbabwe with material provided by South Africa, has established, and is proving a successful biocontrol agent in these countries also (Cilliers et al., 2003).
S. rufinasus has been present in the UK since it was first reported there by Janson (1921) and was probably brought into Europe with the plant. Since then it has been recorded in Ireland, France, Belgium, the Netherlands and Spain (Pratt et al 2013). This agent has been used as in an augmentive manner in England and Ireland and is under consideration for mass-rearing and releasing in the Netherlands, France and Belgium (Pratt et al., 2013).
Case Study:A. filiculoides in South Africa
A. filiculoides was first recorded in South Africa in 1948 from the Oorlogspoort River in the Northern Cape Province of South Africa (30°37’58.22”S 25°21’28.89”E), and by 1999 it was recorded from 152 sites in South Africa, largely in the Free State Province.
Owing to the adverse environmental and economic effects of the weed, a biological control programme was initiated with the importation of the weevil Stenopelmus rufinasus Gyllenhal (Coleoptera: Curculionidae) from Florida, USA, in 1995. Following host-specificity testing, the weevils were released in South Africa in 1997. By 2004, nearly 25,000 weevils had been released throughout South Africa, and their feeding damage has resulted in local extinctions of A. filiculoides from the majority of sites that were surveyed at the time. It took, on average, ten months for a site to be cleared after release of the weevils. The dispersal abilities of the weevils were originally underestimated, but they are capable of dispersing up to 350 km unaided.
Just five years after the release of the weevils, A. filiculoides was no longer considered a threat to South African water bodies (McConnachie et al., 2004). These successes were carefully monitored between 1999 and 2006, documenting the rapid control of the plant, and proving that just four years after the studies by McConnachie et al. (2004) the weevils had succeeded in controlling A. filiculoides at every site where they had been released (Hill et al., 2008).
Country-wide surveys from 2008 produced further evidence of the success of this program. In 2010, of the 102 A. filiculoides sites investigated (40% of water weed sites surveyed), the weed was present at 19 (19%) of these sites, and S. rufinasus was recorded from 14 (73%) of the infested sites. A. filiculoides is no longer a significant problem in South Africa, and where it does occur, S. rufinasus is usually present. Biological control of A. filiculoides is now widely regarded as the most successful biological control programme against an invasive alien weed in South Africa (Coetzee et al., 2011).
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