Invasive plants: addition of Senecio inaequidens and two Ludwigia species to the EPPO Alert List
During its studies, the EPPO Panel on Invasive Alien Species decided that Ludwigia peploides, L. uruguayensis and Senecio inaequidens should be added to the EPPO Alert List, as they have already shown a high potential of invasiveness.
Ludwigia peploides and L. uruguayensis (=L. grandiflora) (Onagraceae – water primroses)
Why: During its studies, the EPPO Panel on Invasive Alien Species decided that Ludwigia peploides and L. uruguayensis should be added to the EPPO Alert List. In particular, their invasiveness has clearly been demonstrated in France during the last 20-30 years.
Description: Perennial aquatic plants which form very dense (almost impenetrable) mats. L. peploides and L. uruguayensis are morphologically very similar and are difficult to differentiate in the absence of flowers. Stems are glabrous to sparsely pubescent. They grow horizontally on water (or mud) and can emerge over the water surface. Leaves are alternate and polymorphic. Early growth consists of rosette-like clusters of rounded leaves on the water surface. At flowering, leaves lengthen to a lanceolate or elliptic shape. Two types of roots are observed: roots which adsorb nutrients and attach the plant to the soil, and adventitious roots located along the stems which ensure oxygen uptake and favour rooting of plant fragments (cuttings). Both species have bright yellow flowers (2-5 cm diameter) with 5 petals, growing from the leaf axils (in France, flowering occurs from June to September). Fruit is a cylindrical capsule of 13-25 mm long and 3-4 mm wide with 5 loculi containing numerous seeds of 1.5 mm. Ludwigia spp. can grow up to 3 m deep in water, and up to 80 cm above water level. These plants have also shown a rather good resistance to frost in Europe.
Pictures can be viewed on Internet:
Where: L. peploides and L. uruguayensis originate from South America, and they can now be found in North America, Africa, Australia and Europe. Data on their geographical distribution is lacking and complicated by the fact that the genus Ludwigia is under revision. As a consequence, the following distribution is only preliminary.
EPPO region: Belgium (few sites), Italy, France (introduced in the 1820-1830s, they remained for a long time within the southern part of France from Camargue to Aquitaine, but they are now spreading towards the north), Netherlands (few sites), Spain (L. grandiflora is mentioned in Flora Iberica), Switzerland (L. grandiflora was observed for the first time in canton of Geneva in summer 2002), United Kingdom (recorded as present but apparently not as an invasive). Both species of Ludwigia are regulated in Portugal (Ministry of Agriculture).
North America: USA (both species are present in many states, see USDA Plant profiles for more details).
South America and Caribbean: Argentina (L. peploides), Cuba (both species).
Oceania: Australia (L. peploides), Chile (L. peploides).
Habitat: Slow-flowing waterways, lakes, ponds, ditches. Ludwigia spp. are also able to colonize river banks and humid pastures (probably due to their high content of saponins and calcium oxalate they are poorly consumed by herbivorous animals).
Damage: The rapid and extensive development of plant populations can block waterways (and thus disturb many human activities such as navigation, hunting, fishing, irrigation and drainage), reduce biodiversity and degrade water quality. Studies done in France have shown that Ludwigia species were able to produce rapidly a high biomass (up to 2 kg of dry matter per m²). Biomass could double in 15 to 20 days in slow-flowing waters, and in 70 days in rivers. As an example, populations of Ludwigia spp. in Marais d’Orx (FR) occupied a few m² in 1993 and reached 130 ha in 1998. In France, these species are considered as dangerous invaders in aquatic or humid environments.
Dispersal: Fragmentation of stems is the main mode of dispersal of Ludwigia spp. The role of seeds remains to be studied further (viable seeds were able to germinate in laboratory conditions but no data has yet been obtained in outdoor conditions). It is suspected that humans and birds are responsible for plant dissemination between waterways. Over long distances, trade for ornamental purposes (aquarium and ponds) can obviously ensure their dissemination.
Pathway: Plants for planting of L. peploides and L. uruguayensis (soil/water containing viable plant fragments or seeds?).
Possible risks: Control is very difficult (mechanical control is possible but care should be taken not to produce more fragments which may disseminate the plants further, herbicides are available but their use in the natural environment is difficult). At least in France, L. peploides and L. uruguayensis have shown a high potential for invasiveness. Further spread of these two species should be avoided.
EPPO RS 2004/119
Panel review date - Entry date 2004-08
Senecio inaequidens (Asteraceae – narrow-leaved ragwort or South African ragwort)
Why: During its studies, the EPPO Panel on Invasive Alien Species decided that Senecio inaequidens should be added to the EPPO Alert List, as this species is still spreading at a rapid pace within Europe.
Description: Perennial plant 40 to 110 cm high, woody at the base. Leaves are alternate, narrow and linear (3 to 14 cm long) and irregularly toothed. Flowers are bright yellow (capitula of 18 to 25 mm diameter with 12 to 14 ligules and numerous disc florets). Achenes of 2 mm with a white pappus are produced in large numbers. S. inaequidens has a high reproductive potential. It is estimated that more than 10,000 seeds are produced per plant and per year, and that seeds may remain viable in the soil for 30-40 years. Germination is rapid and massive, and can take place during most of the year. Germination is also favoured by compacted soils.
Pictures can be viewed on Internet
Where: S. inaequidens originates from South Africa, and was introduced into Europe with imports of wool. Its presence was first recorded in 1889 in Germany, 1922 in Belgium, 1928 in Scotland, 1935 in France and 1947 in Italy. From these foci, S. inaequidens started to spread to other European countries in the 1970s.
EPPO region: Andorra, Belgium, Czech Republic, Denmark, Finland, France, Germany, Italy, Netherlands, Norway, Poland, Spain, Sweden, Switzerland, United Kingdom (including Northern Ireland).
Africa: Botswana, Lesotho, Mozambique, Namibia, South Africa, Swaziland.
South America: Argentina, Colombia (unconfirmed), Mexico (probably a recent introduction).
Habitat: S. inaequidens has a wide range of habitats but it prefers well-drained and disturbed soils. It can be found from coastal to mountain areas (up to 1900 m altitude). It grows along roads and railways, river banks, wastelands. It is also found in forests (in open places after logging or a fire), in crops (particularly grapevine), fallows, pastures. It can survive in most soils (even salty), it can stand hot and dry summers and overwinter in areas where temperatures reach
Damage: S. inaequidens is considered as an invasive species. Its dense populations may reduce biodiversity. However, the impact on biodiversity would need further studies, as S. inaequidens often colonizes ruderal habitats as a ‘pioneer’ plant. In addition, it has been reported as a weed in vineyards and pastures (as it contains toxic alkaloids, it is not eaten by animals).
Dispersal: Dispersal is ensured by achenes which are produced in large numbers. Achenes are mainly transported by wind, but also by water, animals and human activities (especially railways). In addition, vegetative propagation can occur by rooting of stems that touch the ground.
Pathway: Soil containing viable seeds of S. inaequidens. It seems that S. inaequidens is a successful hitch-hiker which can be transported by various ‘hosts’ (containers, vehicles, agricultural machinery, wool, animals…)
Possible risks: In Europe, S. inaequidens has shown its ability to spread and develop large populations in many different habitats. Control measures are available (mechanical or chemical control, studies are needed to assess the efficacy of the aphid Aphis jacobaeae against S. inaequidens as a biocontrol agent) but may not be easy to apply in practice. It is considered as a weed in vineyards and pastures. Further studies are needed on its impact on biodiversity.
EPPO RS 2004/119
Panel review date - Entry date 2004-08
Cordo, H.A.; DeLoach, C.J. (1982) The flee beetle, Lysathia flavipes, that attacks Ludwigia (water primrose) and Myriophyllum (parrotfeather) in Argentina. Coleopterists Bulletin, 36(2), 298-301 (abst.)
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Ministry of Agriculture, PT. Decreto-Lei n.º 565/99. DR 295/99 SÉRIE I-A de 1999-12-21. Ministério do Ambiente Regula a introdução na natureza de espécies não indígenas da flora e da fauna. http://www.idrha.min-agricultura.pt/ruris/legislacao/dl_565_99.htm
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USDA Natural Resources Conservation Service. Plant Profiles. Ludwigia peploides, L. uruguayensis. http://plants.usda.gov
CABI Crop Protection Compendium, 2004.
Rzedowski, J.; Vibrans, H. Calderon de Rzedowski, G.; (2003) Senecio inaequidens D.C. (Compositae, Senecioneae), a harmful weed introduced into Mexico. Acta Botanica Mexicana, no. 63, 83-96 (abst.).
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Agence Méditerranéenne de l’Environnement – Fiche no. 15. Senecio inaequidens. http://www.ame-lr.org/plantesenvahissantes/
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