Taxonomy
Egeria densa | Large-flowered Waterweed
Distribution
Status
Conservation status
Not Assessed
Legal status
Third Schedule listed species under Regulations 49 & 50 in the European Communities (Birds and Natural Habitats) Regulations 2011. (Note: Regulation 50 not yet enacted).
First reported in the wild
1988
Invasiveness
Invasive species - risk of Medium Impact
Irish status
Occasionally present, casual, vagrant, migratory
Introduction pathways - 1
Escape from Confinement
Introduction pathways subclass - 1
Ornamental purpose
Invasive score
17
NAPRA Ireland risk assessed
Yes: This
species underwent a Non-native species APplication
based Risk Analysis in 2014.
Overall
risk of this species to Ireland is categorised as: MODERATE to MAJOR
with a MEDIUM level of confidence.
Overall conclusion summary: Egeria densa has already demonstrated its ability to establish a transient population in the wild in Ireland. Its capacity to cause negative impacts in a number of countries where it has established has also been documented. What is uncertain is how invasive this plant may or may not become should it become established in other suitable waters in Ireland. Closely related Hydrocharitaceae such as Lagarosiphon major and Elodea nuttallii have caused notable ecological and socio-economic impacts in the country (Caffrey et al. 2011 and Caffrey et al. 2006, respectively) and Egeria densa has the potential to emulate this. Therefore, with the limited information available to inform this risk assessment and in acknowledgement of the knowledge gaps that exist, the overall risk of this organism in Ireland is presently considered to be ‘moderate to major’ with ‘medium confidence’
View the full risk assessment: http://nonnativespecies.ie/wp-content/uploads/2014/03/Egeria-densa-Large-flowered-Waterweed1.pdfSpecies Biology
Identification
Dark green, submerge red, evergreen, perennial, macrophyte (aquatic plant large enough to be seen with the nake eye), typically much larger than Elodea spp. (Booy et al., 2015).Round stem, 1-3mm in diameter with leaves in whorls of 4-6, 15-40mm long and bent back towards the stem (Booy et al., 2015).
Ecology
Egeria densa operates as an ecosystem engineer preventing the re-suspension of sediments and controlling the growth of phytoplankton by removing nutrients from the water column (Yarrow et al., 2009) and lowers seed number and seed species richness in areas where it is present (de Winton & Clayton, 1996). Additionally it can outcompete native vegetation (Yarrow et al., 2009), negatively affecting the presence of Myriophyllum spicatum & Potamogeton crispus, though in warmer climate of California, (Santos et al., 2011). It outcompetes two non native aquatic plants Elodea canadensis (Riis et al., 2012; Santos et al., 2011) & Lagarosiphon major (Riis et al., 2012) though this may be temperature dependent with E. densa dominating warmer, shallower waters and L. major dominating colder, clear-water lake (Riis et al., 2012). This may affect patterns of invasion and national distribution of both species. It is known for clogging waterways and hydroelectric turbines (Yarrow et al., 2009) and is difficult to eradicate with a low number of herbivores feeding on it in its native range (Walsh et al., 2012), though one studies concluded a 6 hour exposure to desiccation kills the macrophyte (Marin et al., 2009).
Habitat
Inland surface waters
Reproduction
E. densa is entomophilous (emergent flowers above the water surface that are insect pollinated) with unisexual flowers (Yarrow et al., 2009), though generally a clonal plant (Riis et al., 2012). E. densa tends to reproduce vegetatively, rather than sexually in its introduced range due to male only plants present in Britain, the USA & New Zealand (Booy et al., 2015; Carter & Sytsma, 2001; Lambertini et al., 2010) with low genetic variability in a number of the introduced populations (Carter & Systma, 2001; Lambertini et al., 2010). Shows high rates of dispersal via vegetative fragments, as well as a high potential to colonize disturbed areas (Riis et al., 2012; Yarrow et al, 2009) and though not as effective coloniser as Elodea canadensis can displace it in areas E. candensis has established (Riis et al., 2012).
Pathway and vector description
Widely sold as an oxygenator or ornamental plant may be present in artificial watercourse, ponds and aquaria. Subsequently introduction into the wild is likely to be by escape during flooding or attached to waterfowl, deliberately introduced or through an 'aquarium dump'. Available from a number of different countries and widely traded in EPPO (European and Mediterranean Plant Protection Organisation) countries (Brunel, 2009).
Mechanism of impact
Competition, Bio-fouling, Other
Broad environment
Freshwater
Habitat description
Submerged marcophyte found in lakes, canals, ponds & slow moving rivers (Booy et al., 2015), usually rooted between 1 to 2 m below the surface though it can survive as floating fragments in the water column (Yarrow et al., 2009) and has been found at 7m depth in Colombia (Carillo et al., 2006).
Species group
Plant
Native region
South America
Distribution
World distribution(GBIF)
Irish distribution
Occasionally present - Rare & Localised. The lake in which the historical record of Egeria densa occurred was checked by Inland Fisheries Ireland staff in 2014 and the lake was found to be free of the plant (Millane & Caffrey, 2014).
Native distribution
Native to the subtropical regions of Brazil, Argentina and Uruguay, it has been introduced to all continents except Antarctica (Yarrow et al., 2009).
Temporal change
Date of first record category
1981-1990
Fifty year date category
1951-2000
Records submitted to Data Centre in 2024
The following map is interactive. If you would prefer to view it full screen then click here.
How can you help
Report any sightings to the National Biodiversity Data Centre. Practice good biosecurity protocols when moving boats and fishing equipment by thoroughly disinfecting all gear. Do not purchase any species, marketed under an "Elodea" name. Do not dump aquatic plants in waterways or stock non-indigenous aquatic plants in outdoor ponds or lakes.
References
Publications
Millane, M. & Caffrey, J. (2014) Risk assessment of Egeria densa Planchon – Large-flowered Waterweed. Report prepared for Inland Fisheries Ireland and the National Biodiversity Data Centre. Reynolds, S.C.P. (2002) A catalogue of alien plants in Ireland. National Botanic Gardens. Glasnevin, Dublin. Stace, C. (1997). New Flora of the British Isles 2nd Edition. Cambridge University Press, Cambridge. Brunel, S. (2009). Pathway analysis: aquatic plants imported in 10 EPPO countries. Bulletin OEPP/EPPO Bulletin 39: 201–213. Booy, O., Wade, M. & Roy, H. (2015) A Field Guide to Invasive Plants & Animals in Britain. Bloomsbury. Carrillo, Y., Guarín, A., & Guillot, G. (2006). Biomass distribution, growth and decay of Egeria densa in a tropical high-mountain reservoir (NEUSA, Colombia). Aquatic botany, 85(1), 7-15. Yarrow, M., Marin, V. H., Finlayson, M., Tironi, A., Delgado, L. E., & Fischer, F. (2009). The ecology of Egeria densa Planchon (Liliopsida: Alismatales): A wetland ecosystem engineer. Revista Chilena de Historia Natural, 82(2), 299-313. Carter, M. C., & Sytsma, M. D. (2001). Comparison of the genetic structure of North and South American populations of a clonal aquatic plant. Biological Invasions, 3(2), 113-118. Lambertini, C., Riis, T., Olesen, B., Clayton, J. S., Sorrell, B. K., & Brix, H. (2010). Genetic diversity in three invasive clonal aquatic species in New Zealand. BMC genetics, 11(1), 52. Marín, V. H., Tironi, A., Delgado, L. E., Contreras, M., Novoa, F., Torres-Gómez, M., Garreaud, R., Vila, I. & Serey, I. (2009). On the sudden disappearance of Egeria densa from a Ramsar wetland site of Southern Chile: a climatic event trigger model. Ecological Modelling, 220(15), 1752-1763. Riis, T., Olesen, B., Clayton, J. S., Lambertini, C., Brix, H., & Sorrell, B. K. (2012). Growth and morphology in relation to temperature and light availability during the establishment of three invasive aquatic plant species. Aquatic botany, 102, 56-64. de Winton, M. D., & Clayton, J. S. (1996). The impact of invasive submerged weed species on seed banks in lake sediments. Aquatic Botany, 53(1), 31-45. Walsh, G. C., Dalto, Y. M., Mattioli, F. M., Carruthers, R. I., & Anderson, L. W. (2013). Biology and ecology of Brazilian elodea (Egeria densa) and its specific herbivore, Hydrellia sp., in Argentina. BioControl, 58(1), 133-147.
Relevant links
Global Invasive Species Database
Risk Assessment of Egeria densa