Hydrocotyle ranunculoides | Floating Pennywort
Third Schedule listed species under Regulations 49 & 50 in the European Communities (Birds and Natural Habitats) Regulations 2011. (Note: Regulation 50 not yet enacted).
Listed as a schedule 9 species under Articles 15 & 15A of the Wildlife Order (Northern Ireland) 1985 (Article 15A not yet enacted).
Regulated invasive species of Union concern under the European Regulation on the prevention and management of the introduction and spread of invasive alien species [1143/2014].
First reported in the wild
Invasive species - risk of High Impact
Introduction pathways - 1
Escape from Confinement
Introduction pathways subclass - 1
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: MAJOR with a HIGH level of confidence.
Overall conclusion summary: Hydrocotyle ranunculoides poses a major risk to native biodiversity, native ecosystems and conservation goals as well as having the potential to cause negative socio-economic impacts in a wide-range of still or slow-flowing waters in Ireland. The plant has a high capacity to establish dense infestations here in suitable habitats which would result in a range of negative impacts as reported from elsewhere in its introduced range. Despite that this species has not arrived in Ireland to date, its ability to spread should not be underestimated. Banning its sale has worked well in Britain, but new sites continue to be recorded each year. (J Newman, personal communication).
View the full risk assessment: http://nonnativespecies.ie/wp-content/uploads/2014/03/Hydrocotyle-ranunculoides-Floating-Pennywort1.pdf
Perennial, with thin rooting stems, often floating. Leaves up to 70mm across on thin, usually erect petioles (Stace, 1997). May be confused with H. vulgaris.
Has the potential to form dense stands and displace native vegetation but to date there are no recorded impacts of this species in Ireland due to its restricted range and management and eradication efforts.
Inland surface waters
Can spread vegetatively and regenerates freely (Hussner & Lösch, 2007).
Pathway and vector description
Sold as an ornamental or oxygenating plant in ponds or aquaria and was likely introduced into the wild in Ireland either as a result of flooding washing the plant into waterways or deliberately by dumping of plant material into water courses (Day, 2004).
Mechanism of impact
There is currently an EU wide ban on the sale, growing and keeping of this plant (European Commission, 2017).
Hand-pulling is effective for small areas but is labour intensive. Containment nets must be used (Angling Trust, undated).
Cutting boats can be useful for large infestations or in conjunction with other methods. Care must be taken not to facilitate spread so the use of capture nets or floating boons is essential.
Raking is usually more effective than cutting as it also removes some of the roots (Angling Trust, undated). Capture nets must be used and the damage to animal and bird habitats must be considered.
A combination of some of the above methods may be appropriate depending on the situation at a particular site. Kelly (2006) reports Hydrocotyle ranunculoides was successfully removed from Gillingham Marshes, Suffolk, England by the use of a digger and then handpicking for the following two years.
The Angling Trust (undated) recommends glyphosate application from March to October. An appropriate and licensed adjuvant is necessary due to the poor chemical uptake by the leaves. This herbcide is non-selective so care must be taken to target only the intended species.
The planting of trees and shrubs can be a useful long-term method. However, the planting should be intermittent and concentrated at points of particular concern (Bentley et al., 2014).
H. ranunculoides is intolerant of water deeper than 1m. (Bentley et al., 2014). The raising of water levels above this could be an effective control measure if the new level can be maintained for an adequate period. However, this method in non-selective and non-target plants may also be affected.
Hydro venturi, uses a combination of water and air to blow roots out of the substrate and has been used in the Netherlands with good success (Bentley et al.). It causes less fragmentation than other removal methods.
Lakes, rivers, canals & other slow moving waterbodies.
Established - Localised. Present in a number of ponds and rivers in counties Antrim and Down, though it has been eradicated from a number of sites (Day, 2004; Millane & Caffrey, 2014).
Native to North America (Millane & Caffrey, 2014).
Date of first record category
Fifty year date category
Records submitted to Data Centre in 2023
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.
Do not purchase this plant or grow in outdoor ponds.
Dispose of garden waste responsibly and never dump aquatic plants in lakes.
Angling Trust. (undated). Floating Pennywort- Hydrocotyle ranunculoides.Information sheet. http://www.nonnativespecies.org/index.cfm?pageid=208 Site accessed 24 August 2017.
Bentley, S; Brady, R; Cooper, J; Davies, K; Hemsworth, M; Robinson, P; Thomas, L. (2014). Aquatic and riparian plant management: controls for vegetation in watercourses. Technical guide. Bristol, Environment Agency, 285pp. (Project SC120008/R2, CEH Project no. C04908). http://nora.nerc.ac.uk/509613/1/N509613CR.pdf Site accessed 28 August 2017.
Day G (2004) Hydrocotyle ranunculoides L. f., an invasive aquatic plant, in Cos Down (H38) and Antrim (H39). Irish Naturalists' Journal 27: 400.
European Commission. (2017). Invasive Alien Species of Union Concern. European Union, Luxembourg.
Hussner, A., & Lösch, R. (2007). Growth and photosynthesis of Hydrocotyle ranunculoides L. fil. in Central Europe. Flora-Morphology, Distribution, Functional Ecology of Plants, 202(8), 653-660.
Hussner, A; Denys, L, and van Valkenburg, J. (2012). NOBANIS – Invasive Alien Species Fact Sheet – Hydrocotyle ranunculoides. Online Database of the European Network on Invasive Alien Species. https://www.nobanis.org/globalassets/speciesinfo/h/hydrocotyle-ranunculoides/hydrocotyle_ranunculoides.pdf Site accessed 24 August 2017.
Kelly, A. (2006). Removal of invasive floating pennywort Hydrocotyle ranunculoides from Gillingham Marshes, Suffolk, England. Conservation Evidence, 3, pp 52 – 53. http://www.conservationevidence.com/reference/download/2220 Site accessed 24 August 2017.
Millane, M. & Caffrey, J. (2014). Risk Assessment of Hydrocotyle ranunculoides Linnaeus filius – Floating Pennywort. Report prepared for Inland Fisheries Ireland and the National Biodiversity Data Centre.
Stace, C. (1997) A New Flora of the British Isles, 2nd edition. Cambridge University Press, Cambridge.