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
Invasive species - risk of High Impact
Introduction pathways - 1
Release in Nature
Introduction pathways subclass - 1
NAPRA Ireland risk assessed
Densely branched evergreen shrub, up to 5m tall, leaves 6-20cm in dense terminal racemes, elliptical to oblong, distinctive mauve/purple flowers 4-6cm across (Stace, 1997).
Crowds out native plants, forming dense monoculture (Barron, 2007) and impacts on community level processes in streams and rivers where it is present (Hladyz et al., 2011). May produce alleopathic chemicals, preventing native species from growing in soil in which it is present (Hulme, 2009). Hosts a fellow invasive species Phytophthora ramorum (Sudden oak death) which can affect a number of tree species (though not Oak) (Brennan et al., 2008). Control costs in the UK cost ~£560 per ha in 2001 (Dehnen-Schmutz et al., 2004). Honey from bees collecting pollen from Rhododendron may be toxic to humans (Hulme, 2009).
Mires, bogs & fens; Grasslands and landscapes dominated by forbs, mosses or lichens; Heath, scrubland & tundra; Woodland, forest and other wooded land; Regularly or recently cultivated agricultural, horticultural or domestic habitat; Constructed, industrial or other artificial habitats; Miscellaneous
Plants set seed at age 12 and can produce over a million seeds per plant (Cross, 1975). Can also spread by layering as branches can root anywhere they touch the ground (Cross, 1975).
Pathway and vector description
Cultivated in Ireland since 1800 (Reynolds, 2002), it is a common garden plant and a wide variety of different Rhododendron breeds and species are sold in Ireland. Spread by seed and layering to its current range.
Mechanism of impact
Competition, Poisoning/Toxicity, Bio-fouling
Found on a wide variety of habitats, woodlands, peaty and sandy soil, grassland and most suitable places, though rare in urban areas (Reynolds, 2002; Stace, 1997). Generally invades disturbed areas as seedlings have difficulty establishing in areas covered by native plants (Hulme, 2009).
Established - Widespread & Common, Rare in urban areas (Reynolds, 2002).
Rhododendron ponticum is native to a number of regions, Iberia, Turkey, southern Russia and the Lebanon but plants found in Britain are thought to descend from the Iberian populations (Milne & Abbott, 2000).
Date of first record category
Records submitted to Data Centre in 2021
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How can you help
Report any sightings to the National Biodiversity Data Centre.
Delivering Alien Invasive Species In Europe (DAISIE) project list rhododendron as one of the 100 Worst Invaders in Europe.
Barron, C. 2007. The Control of Rhododendron in Native Woodlands. In: LITTLE, D. (ed.) Native Woodland Scheme Information Note No. 3. Forest Service: Woodlands of Ireland Coillearnacha.
Brennan J, Cummins D, Kearney S, Choiseul J, Cahalane G, & Nolan S (2008) Investigating the threat of Phytophthora ramorum to Ireland; the current situation. Phytopathology 98(6 suppl.).
Cross, J. R. (1975). Rhododendron Ponticum L. The Journal of Ecology, 345-364. Hulme, P. (2009). Rhododendron ponticum L., rhododendron (Ericaeae, Magnoliophyta). In: DAISIE (ed.) The Handbook of European Alien Species. Springer, Dordrecht.
Dehnen-Schmutz, K., Perrings, C., & Williamson, M. (2004). Controlling Rhododendron ponticum in the British Isles: an economic analysis. Journal of Environmental Management, 70(4), 323-332.
Hladyz, S., Åbjörnsson, K., Giller, P. S., & Woodward, G. (2011). Impacts of an aggressive riparian invader on community structure and ecosystem functioning in stream food webs. Journal of Applied Ecology, 48(2), 443-452.
Milne, R. I., & Abbott, R. J. (2000). Origin and evolution of invasive naturalized material of Rhododendron ponticum L. in the British Isles. Molecular Ecology, 9(5), 541-556.
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.