EPPO Alert List – Vallisneria australis (Hydrocharitaceae)
Why
Vallisneria australis (Hydrocharitaceae) has been known from the EPPO region since the 1800s though it has more recently been recorded as a species with invasive behaviour. The EPPO Panel on Invasive Alien Plants are seeking further information on any additional occurrences of V. australis in the EPPO region and reports of environmental and economic impacts.
Young plant. Courtesy: Guillaume Fried
In Lake Salagou (FR). Courtesy: Guillaume Fried
Invaded area (Lake Salagou, FR). Courtesy: Guillaume Fried
Geographical distribution
Asia: Japan.
EPPO region: Belgium, France, Germany, Hungary, Italy, the Netherlands
North America: USA (California).
Oceania: Australia (Native), New Zealand.
Morphology
Vallisneria australis is a rooted submerged freshwater aquatic perennial species. The long elongate strap-shaped leaves can be up to 3 metres long and 1.5-3.5 cm wide, with fine toothed margins towards the leaf apex. The 5-7 prominent longitudinal leaf veins are parallel and connected by small lateral veins. The species is dioecious. Small male flowers (< 0.5 mm) are clustered in membranous sheaths near the bases of the male plants and are released to float to the water surface. The small 3-parted female flowers are approximately 2-4 mm long, generally borne singly (sometimes up to 4 per inflorescence) in a tubular sheath at the end of a long narrow stalk (peduncle).
Biology and Ecology
Vallisneria australis has been reported to grow in waterbodies up to 6 m in depth. It can grow in still and moderately fast-flowing water bodies. Male and female plants are reported in the EPPO region though they are not currently reported to occur together in the same area.
Habitats
In its native range, V. australis is found in rivers, streams and other inland water bodies. In the EPPO region it is present in thermally heated canals in Hungary and is present in modified water bodies (rice fields, canals and gravel pits) in Belgium, the Netherlands, Germany and Italy. In France, it has been present for at least 10 years and occurs in two artificial water bodies located far apart, Lake Salagou (Hérault) and Lake Vaivre, near Vesoul (Haute-Saône).
Pathways for movement
Vallisneria australis has entered the EPPO region as an ornamental aquarium plant, mostly under an incorrect name. Natural spread is via vegetative plant fragmentation and seed (though it is not known if viable seed is produced in the EPPO region), dispersed by the water flow. Spread can also be facilitated via human assistance, e.g. boats or dredging equipment.
Impacts
Observations in Hungary detail that V. australis is a strong competitor and can replace other submerged invasive alien plants such as Hydrilla verticillata (Hydrocharitaceae: EPPO List of Invasive Alien Plants) and Cabomba caroliniana (Cabombaceae: EPPO List of Invasive Alien Plants). The species can form dense populations and in France they have been reported to occur over several thousand square metres. Native plant species and higher trophic levels can be negatively impacted as the long leaves can act to shade out sunlight altering the chemical composition of the waterbody. The species could block drainage ditches.
Control
Controlling V. australis is difficult and would likely be similar to other submerged species where physical removal is applied. However, removing all of the biomass of a population would be very problematic due to the habitat.
Sources
Dutartre A (2022) Vallisneria australis, une nouvelle espèce aquatique exotique en France. http://especes-exotiques-envahissantes.fr/vallisneria-australis-une-nouvelle-espece-aquatique-exotique-en-france/
EPPO (2023) First record of Vallisneria australis in France. EPPO Reporting Service 2023/026. https://gd.eppo.int/reporting/article-7508
Mesterházy A, Somogyi G, Efremov A, Verloove V (2021) Assessing the genuine identity of alien Vallisneria (Hydrocharitaceae) species in Europe. Aquatic Botany 174, 103431, 6 pp.