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''Rhododendron ponticum'', called common rhododendron or pontic rhododendron, is a species of ''
Rhododendron ''Rhododendron'' (; from Ancient Greek ''rhódon'' "rose" and ''déndron'' "tree") is a very large genus of about 1,024 species of woody plants in the heath family (Ericaceae). They can be either evergreen or deciduous. Most species are nati ...
'' native to the
Iberian Peninsula The Iberian Peninsula (), ** * Aragonese and Occitan: ''Peninsula Iberica'' ** ** * french: Péninsule Ibérique * mwl, Península Eibérica * eu, Iberiar penintsula also known as Iberia, is a peninsula in southwestern Europe, defi ...
in southwest
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
and the
Caucasus The Caucasus () or Caucasia (), is a region between the Black Sea and the Caspian Sea, mainly comprising Armenia, Azerbaijan, Georgia, and parts of Southern Russia. The Caucasus Mountains, including the Greater Caucasus range, have historically ...
region in northern
West Asia Western Asia, West Asia, or Southwest Asia, is the westernmost subregion of the larger geographical region of Asia, as defined by some academics, UN bodies and other institutions. It is almost entirely a part of the Middle East, and includes Ana ...
.


Description

''R. ponticum'' is a dense,
suckering Basal shoots, root sprouts, adventitious shoots, and suckers are words for various kinds of shoots that grow from adventitious buds on the base of a tree or shrub, or from adventitious buds on its roots. Shoots that grow from buds on the base o ...
shrub A shrub (often also called a bush) is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees ...
or small
tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...
growing to tall, rarely . The
leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...
are
evergreen In botany, an evergreen is a plant which has foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with deciduous plants, which ...
, long and wide. The
flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechani ...
s are in diameter, violet-purple, often with small greenish-yellow spots or streaks. The
fruit In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering. Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particu ...
is a dry capsule long, containing numerous small
seed A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiospe ...
s. It has two
subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...
: *''R. p. baeticum'' (Boiss. & Reut.) Hand.-Mazz. – Found in central and southern
Portugal Portugal, officially the Portuguese Republic ( pt, República Portuguesa, links=yes ), is a country whose mainland is located on the Iberian Peninsula of Southwestern Europe, and whose territory also includes the Atlantic archipelagos of ...
and southern
Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , i ...
(in the
Province of Cádiz Cádiz is a Provinces of Spain, province of southern Spain, in the southwestern part of the Autonomous communities of Spain, autonomous community of Andalusia. It is the southernmost part of mainland Spain, as well as the southernmost part of conti ...
). *''R. p. ponticum'' – Found around the southern
Black Sea Basin The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Roma ...
(eastern
Bulgaria Bulgaria (; bg, България, Bǎlgariya), officially the Republic of Bulgaria,, ) is a country in Southeast Europe. It is situated on the eastern flank of the Balkans, and is bordered by Romania to the north, Serbia and North Macedon ...
, northern
Turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a list of transcontinental countries, transcontinental country located mainly on the Anatolia, Anatolian Peninsula in Western Asia, with ...
,
Georgia Georgia most commonly refers to: * Georgia (country), a country in the Caucasus region of Eurasia * Georgia (U.S. state), a state in the Southeast United States Georgia may also refer to: Places Historical states and entities * Related to the ...
,
Northern Caucasus The North Caucasus, ( ady, Темыр Къафкъас, Temır Qafqas; kbd, Ишхъэрэ Къаукъаз, İṩxhərə Qauqaz; ce, Къилбаседа Кавказ, Q̇ilbaseda Kavkaz; , os, Цӕгат Кавказ, Cægat Kavkaz, inh, ...
) and central
Lebanon Lebanon ( , ar, لُبْنَان, translit=lubnān, ), officially the Republic of Lebanon () or the Lebanese Republic, is a country in Western Asia. It is located between Syria to the north and east and Israel to the south, while Cyprus li ...
. And a
variegated Variegation is the appearance of differently coloured zones in the leaves and sometimes the stems and fruit of plants. Species with variegated individuals are sometimes found in the understory of tropical rainforests, and this habitat is the s ...
variety: *''R. p. var. heterophyllum'' R. Ansin – Found in
Turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a list of transcontinental countries, transcontinental country located mainly on the Anatolia, Anatolian Peninsula in Western Asia, with ...
.


Distribution and habitat

The species has two disjunct populations, one in the southwestern
Iberian Peninsula The Iberian Peninsula (), ** * Aragonese and Occitan: ''Peninsula Iberica'' ** ** * french: Péninsule Ibérique * mwl, Península Eibérica * eu, Iberiar penintsula also known as Iberia, is a peninsula in southwestern Europe, defi ...
(central and southern
Portugal Portugal, officially the Portuguese Republic ( pt, República Portuguesa, links=yes ), is a country whose mainland is located on the Iberian Peninsula of Southwestern Europe, and whose territory also includes the Atlantic archipelagos of ...
and southwestern
Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , i ...
) and the other near the southern
Black Sea Basin The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Roma ...
(eastern
Bulgaria Bulgaria (; bg, България, Bǎlgariya), officially the Republic of Bulgaria,, ) is a country in Southeast Europe. It is situated on the eastern flank of the Balkans, and is bordered by Romania to the north, Serbia and North Macedon ...
, northern
Turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a list of transcontinental countries, transcontinental country located mainly on the Anatolia, Anatolian Peninsula in Western Asia, with ...
,
Georgia Georgia most commonly refers to: * Georgia (country), a country in the Caucasus region of Eurasia * Georgia (U.S. state), a state in the Southeast United States Georgia may also refer to: Places Historical states and entities * Related to the ...
, and
Northern Caucasus The North Caucasus, ( ady, Темыр Къафкъас, Temır Qafqas; kbd, Ишхъэрэ Къаукъаз, İṩxhərə Qauqaz; ce, Къилбаседа Кавказ, Q̇ilbaseda Kavkaz; , os, Цӕгат Кавказ, Cægat Kavkaz, inh, ...
). It has also been introduced to
Madeira ) , anthem = ( en, "Anthem of the Autonomous Region of Madeira") , song_type = Regional anthem , image_map=EU-Portugal_with_Madeira_circled.svg , map_alt=Location of Madeira , map_caption=Location of Madeira , subdivision_type=Sovereign st ...
,
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
,
Belgium Belgium, ; french: Belgique ; german: Belgien officially the Kingdom of Belgium, is a country in Northwestern Europe. The country is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeast, France to th ...
,
England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...
,
France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
and
Ireland Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...
. The range in the Iberian Peninsula is limited to mountain ranges, the Caramulo mountains, the Monchique range and the Aljibe range. A remnant of the original
laurissilva Laurel forest, also called laurisilva or laurissilva, is a type of subtropical forest found in areas with high humidity and relatively stable, mild temperatures. The forest is characterized by broadleaf tree species with evergreen, glossy and elo ...
forests that covered the peninsula 66 million years ago. Though the common rhododendron was present in
Great Britain Great Britain is an island in the North Atlantic Ocean off the northwest coast of continental Europe. With an area of , it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It is ...
prior to the most recent ice age, it did not recolonise afterwards and the modern ecology of the island developed without it. Its presence today in Great Britain is due to humans introducing it, and it easily naturalises and becomes a pest in some situations, often covering whole hillsides (especially in
Snowdonia Snowdonia or Eryri (), is a mountainous region in northwestern Wales and a national park of in area. It was the first to be designated of the three national parks in Wales, in 1951. Name and extent It was a commonly held belief that the nam ...
and the western British Isles). In the British Isles, it colonises moorlands, uplands, shady woodlands (alongside escaped laurels and the native holly) and in areas of acid soils, often in shaded areas.


Historical range

Fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
evidence shows it had a much wider range across most of southern and western Europe before the
Late Glacial Maximum The Last Glacial Maximum (LGM), also referred to as the Late Glacial Maximum, was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent. Ice sheets covered much of Northern North America, Northern Eur ...
, or until about 20,000 years ago. It was noted by the botanist
Joseph Pitton de Tournefort Joseph Pitton de Tournefort (5 June 165628 December 1708) was a French botanist, notable as the first to make a clear definition of the concept of genus for plants. Botanist Charles Plumier was his pupil and accompanied him on his voyages. Lif ...
during his travels in the Near East in 1700–02, and so received its name from
Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...
to identify the ancient kingdom on the south shores of the
Black Sea The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Roma ...
,
Pontus Pontus or Pontos may refer to: * Short Latin name for the Pontus Euxinus, the Greek name for the Black Sea (aka the Euxine sea) * Pontus (mythology), a sea god in Greek mythology * Pontus (region), on the southern coast of the Black Sea, in modern ...
, in which it grew. At the other end of its range, in southern Spain, Linnaeus' friend and correspondent
Clas Alströmer Baron Clas Alströmer (9 August 1736 – 5 March 1794) was a Swedish naturalist who was a student of Carl Linnaeus at Uppsala University. From 1760 to 1764 he traveled throughout Southern Europe, collecting plants for Linnaeus. He established a bot ...
found it growing with
oleander ''Nerium oleander'' ( ), most commonly known as oleander or nerium, is a shrub or small tree cultivated worldwide in temperate and subtropical areas as an ornamental and landscaping plant. It is the only species currently classified in the ge ...
. It was introduced to Britain as an ornamental
shrub A shrub (often also called a bush) is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees ...
in 1763, and later planted as cover for game birds. It is now considered to be an
invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...
.


Cultivation and uses

''Rhododendron ponticum'' subsp. ''baeticum'' is one of the most extensively cultivated rhododendrons in western Europe. It is used as an
ornamental plant Ornamental plants or garden plants are plants that are primarily grown for their beauty but also for qualities such as scent or how they shape physical space. Many flowering plants and garden varieties tend to be specially bred cultivars that i ...
in its own right, and more frequently as a
rootstock A rootstock is part of a plant, often an underground part, from which new above-ground growth can be produced. It could also be described as a stem with a well developed root system, to which a bud from another plant is grafted. It can refer to a ...
onto which other more attractive rhododendrons are
grafted Grafting or graftage is a horticultural technique whereby tissues of plants are joined so as to continue their growth together. The upper part of the combined plant is called the scion () while the lower part is called the rootstock. The succ ...
. The plants were first grown in Britain in the 1760s, supplied by Conrad Loddiges, and became widely distributed through the commercial nursery trade in the late 18th and early 19th centuries. The roots readily send up suckers from below the graft, often allowing it to overtake the intended grafted rhododendron. Honey produced with pollen from the flowers of this plant can be quite poisonous, causing severe
hypotension Hypotension is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Blood pressure is indicated by two numbers, the systolic blood pressure (the top number) and the dias ...
and
bradycardia Bradycardia (also sinus bradycardia) is a slow resting heart rate, commonly under 60 beats per minute (BPM) as determined by an electrocardiogram. It is considered to be a normal heart rate during sleep, in young and healthy or elderly adults, a ...
in humans if consumed in sufficient quantities, due to toxic diterpenes (
grayanotoxin Grayanotoxins are a group of closely related neurotoxins named after '' Leucothoe grayana'', a plant native to Japan originally named for 19th century American botanist Asa Gray. Grayanotoxin I (grayanotaxane-3,5,6,10,14,16-hexol 14-acetate) is als ...
s).


Invasive species

Suckering of the root, together with its abundant seed production, has led to it becoming an
invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...
over much of western Europe and in parts of
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
. Rhododendron control is a key element in nature conservation in those areas. Conservation organisations in Britain now believe ''R. ponticum'' has become "a severe problem" in the native
Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...
oak An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably ''L ...
woods of the
west highlands The Highlands ( sco, the Hielands; gd, a’ Ghàidhealtachd , 'the place of the Gaels') is a historical region of Scotland. Culturally, the Highlands and the Lowlands diverged from the Late Middle Ages into the modern period, when Lowland ...
of
Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...
and in
Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...
, and on
heathland A heath () is a shrubland habitat found mainly on free-draining infertile, acidic soils and characterised by open, low-growing woody vegetation. Moorland is generally related to high-ground heaths with—especially in Great Britain—a cooler ...
s in southern
England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...
, crowding out the native flora. Clearance strategies have been developed, including the flailing and cutting down of plants with follow-up
herbicide Herbicides (, ), also commonly known as weedkillers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page fo ...
spraying. Injection of herbicide into individual plants has been found to be more precise and effective. A study in the journal ''
Functional Ecology Functional ecology is a branch of ecology that focuses on the roles, or functions, that species play in the community or ecosystem in which they occur. In this approach, physiological, anatomical, and life history characteristics of the species a ...
'' also showed that invasive rhododendron nectar was toxic to European honeybees (''
Apis mellifera The western honey bee or European honey bee (''Apis mellifera'') is the most common of the 7–12 species of honey bees worldwide. The genus name ''Apis'' is Latin for "bee", and ''mellifera'' is the Latin for "honey-bearing" or "honey carrying", ...
''), killing individuals within hours of consumption. It also paralyzed bees of the species '' Andrena carantonica'' (no named ''A. scotica'', a solitary mining bee. Bees became paralysed and exhibited excessive grooming or other distress behaviours after feeding on Rhododendron nectar, and ate less food than bees fed a control nectar. In contrast the buff-tailed bumblebee (''
Bombus terrestris ''Bombus terrestris'', the buff-tailed bumblebee or large earth bumblebee, is one of the most numerous bumblebee species in Europe. It is one of the main species used in greenhouse pollination, and so can be found in many countries and areas wher ...
'') was not affected by the rhododendron nectar. It is important not to see Rhododendron as a problem species for honey bees as they actually avoid the flowers owing to their ability to detect the toxin nectar. The toxicity is caused by
grayanotoxin Grayanotoxins are a group of closely related neurotoxins named after '' Leucothoe grayana'', a plant native to Japan originally named for 19th century American botanist Asa Gray. Grayanotoxin I (grayanotaxane-3,5,6,10,14,16-hexol 14-acetate) is als ...
1 which is one of several highly hydroxylated diterpenoid defence chemicals produced in the leaves of ''Rhododendron'' to protect against
herbivores A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
- e.g. the
Thrips Thrips ( order Thysanoptera) are minute (mostly long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Different thrips species feed mostly on plants by puncturing and sucking up the contents, although a few are ...
''Heliothrips haemorrhoidalis''. Some species of honey bee (''Apis mellifera'' sub spp ''caucasica'') tolerate the toxin and make so called mad-honey. Identification difficulties Recent efforts to manage the spread of rhododendron ponticum in the United Kingdom has led to some controversy, particularly within the grounds of Taymouth castle in highland Perthshire. There remains debate over appropriate identification of the plant, particularly where it is interspersed amongst clumps of Japanese Laurel (Aucuba Japonica) in areas of mixed woodland. Tensions surrounding the management of these cohabiting species were brought to a head in early December 2022 when prominent arboriculturalists faced strong opposition from machine operators within the estate over correct identification and subsequent management of the plant, culminating in the destruction of a large thicket of laurel. While there remains debate over the associated similarities and differences between the plants, contemporary research indicates the likelihood of a hybridisation between the two species in this niche of woodland, meaning that Japanese laurel may indeed be viewed and treated in a like manner to rhododendron within this habitat niche.Milne, R.I. and Abbott, R.J., 2000. Origin and evolution of invasive naturalized material of Rhododendron ponticum L. in the British Isles. Molecular Ecology, 9(5), pp.541-556.


See also

*
Catawbiense hybrid A catawbiense hybrid is a hybrid of the plant genus '' Rhododendron'', derived from crosses of American species '' Rhododendron catawbiense'' and ''Rhododendron maximum'' with European and Asian species '' R. arboreum'', '' R. caucasicum'' and ...
– hybrid with R.ponticum


References


External links


Flora Europaea: ''Rhododendron ponticum''
* * ttps://web.archive.org/web/20061011234354/http://www.ccs.st-and.ac.uk/rhodo.php Centre for Conservation Strategy: ''Rhododendron ponticum'' in Britainbr>Danish Rhododendron Society: ''Rhododendron ponticum'' in Europe
*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: 541–55
Abstract
{{Taxonbar, from=Q557928 ponticum Flora of Bulgaria Flora of Georgia (country) Flora of Lebanon Flora of Portugal Flora of Russia Flora of Spain Flora of Turkey Plants described in 1762 Taxa named by Carl Linnaeus