Rhododendron
ponticum
Taxon
Rhododendron ponticum L.
Family / Order / Phylum
Ericaceae / Ericales / Plantae
COMMON NAMES (English only)
Rhododendron
SYNONYMS
Rhododendron speciosum (Willd.) Sweet.
Rhododendron lancifolium Moench.
SHORT DESCRIPTION
This evergreen shrub is densely branched growing to
5m. Flowers, borne in racemes of 10-15, are violet to
purple. Pollination by insects results in the production
of numerous small seeds within a woody capsule.
BIOLOGY/ECOLOGY
Dispersal mechanisms
The small seeds are dispersed up to 100 m by
wind and water under favourable open
Rhododedron ponticum in flower
conditions, but often less far in closed canopy
Photo: www.aphotoflora.com
forest.
Reproduction
Flowers are pollinated by bees, hoverflies and butterflies. Each flower head can produce between three thousand
and seven thousand seeds, so that a large bush can produce several million seeds per year. Seeds require light for
germination. Vegetative reproduction is limited, ends of branches may root if in contact with soil but such
growth is usually only found at forest edges.
Known predators/herbivores
Potentially toxic chemicals, particularly 'free' phenols, and diterpenes, occur in significant quantities in the
tissues of rhododendron, such that foliage is unpalatable to vertebrates and few insects feed on the plant.
Resistant stages (seeds, spores etc.)
Seeds in the soil can remain viable for several years.
HABITAT
Native (EUNIS code)
G1: Mixed deciduous forest
Habitat occupied in invaded range (EUNIS code)
G1: Mixed deciduous forest, F4: Temperate heaths, D1: Raised and blanket bogs
Habitat requirements
Tolerant of a wide range of temperatures but intolerant to drought. It grows best in uniformly damp climates.
Seedlings have difficulty becoming established in areas where there is already continuous ground cover from
native plants. Establishment is best in disturbed areas where the native vegetation has been in some way
disrupted, providing an opening in the plant cover.
DISTRIBUTION
Native Range
A disjunct distribution. R. ponticum ssp. baeticum is found in south-west Spain and southern Portugal, whereas
ssp. ponticum is found in Turkey, Lebanon, Bulgaria and the Caucasus.
Known Introduced Range
Naturalised in the United Kingdom, Ireland, Belgium, France and Netherlands. Present in Austria.
Trend
There is increasing invasion in continental Europe.
MAP (European distribution)
Known in country
Legend
Known in CGRS square
Known in sea
Native in country
Native in CGRS square
Assumed native range
INTRODUCTION PATHWAY
It was introduced and widely planted as an ornamental in large landscaped gardens by Victorian Rhododendron
enthusiasts and subsequently taken up in smaller gardens. It is still available from nurseries.
IMPACT
Ecosystem Impact
Once rhododendron has invaded an area, few native plants survive. In woodlands, only those trees which manage
to grow above the level of the rhododendron canopy will persist. When such trees die, they cannot be replaced
because seedlings cannot become established under the lightless canopy. At this point, the rhododendron
completely dominates the area. Stands accumulate thick litter layers.
Health and Social Impact
Anecdotal information suggests that honey from rhododendron is toxic to humans. This is known as 'Honey
intoxication' and results in relatively short-lived intestinal and cardiac problems but is rarely fatal. The severity
of symptoms depends on the amount of contaminated honey consumed.
Economic Impact
It is considered a problem in commercial forests and moorlands managed for gamebirds.
MANAGEMENT
Prevention
Avoid planting as an ornamental.
Mechanical
Plants sprout vigorously after cutting. Mechanical clearance involves a tracked swing shovel with a rotary flail
mounted on a moving hydraulic arm. In sensitive conservation areas, such techniques may well not be
appropriate. Such mechanical devices often leave a thick layer of smashed rhododendron on the ground that may
have to be removed using manual labour.
Chemical
The leaves are waxy and herbicide treatment must include a chemical additive to help break this surface down.
Usually spraying is ineffective. Glyphosate injection into root stumps should be combined with mechanical
clearing.
Biological
Unknown.
REFERENCES
Cross JR (1975) Biological flora of the British Isles. Rhododendron ponticum L J Ecol 63:345-364
Erfmeier A, Bruelheide B (2004) Comparsion of native and invasive Rhododendron ponticum populations: Growth,
reproduction and morphology under field conditions, Flora 199:120-133
Tyler C, Pullin AS, Stewart GB (2006) Effectiveness of management interventions to control invasion by
Rhododendron ponticum. Env Management 37:513-522
OTHER REFERENCES
Dehnen-Schmutz K, Perrings C, Williamson M (2004) Controlling Rhododendron ponticum in the British Isles: an
economic analysis. J.Env Management 70:323-332
Dixon FL, Clay DV (2002) Imazapyr application to Rhododendron ponticum: speed of action and effects on other
vegetation. Forestry 75:217-225
Erfmeier A, Bruelheide H (2005) Invasive and native Rhododendron ponticum populations: is there evidence for
genotypic differences in germination and growth? Ecography 28:417-428
Stephenson CM, MacKenzie ML, Edwards C, Travis JMJ (2006) Modelling establishment probabilities of an exotic
plant, Rhododendron ponticum, invading a heterogeneous, woodland landscape using logistic regression with
spatial autocorrelation. Ecol Mod 193:747-758
Stout JC, Parnell J, Arroyo J, Crowe TP (2006) Pollination ecology and seed production of Rhododendron ponticum
in native and exotic habitats. Biodivers Cons 15:755-777
Yildiz O, Esen D (2006) Effects of different Rhododendron control methods in eastern beech (Fagus orientalis
Lipsky) ecosystems in the western Black Sea region of Turkey. Ann Appl Biol 149:235-242
Author: Phil Hulme
Date Last Modified: November 9th, 2006