Common Rhododendron

Appearance

''R. ponticum'' is a dense, suckering shrub or small tree growing to 5 m tall, rarely 8 m . The leaves are evergreen, 6 to 18 cm long and 2 to 5 cm wide. The flowers are 3.5 to 5 cm in diameter, violet-purple, often with small greenish-yellow spots or streaks. The fruit is a dry capsule 1.5 to 2.5 cm long, containing numerous small seeds.

It has two subspecies:
⤷ ''R. p. baeticum'' Hand.-Mazz. – Found in central and southern Portugal and southern Spain .
⤷ ''R. p. ponticum'' – Found around the southern Black Sea Basin and central Lebanon.

And a variegated variety:
⤷ ''R. p. var. heterophyllum'' R. Ansin – Found in Turkey.

Naming

Suckering of the root, together with its abundant seed production, has led to it becoming an invasive species over much of western Europe and in parts of New Zealand. 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 oakwoods of the west highlands of Scotland and in Wales, and on heathlands in southern England, crowding out the native flora. Clearance strategies have been developed, including the flailing and cutting down of plants with follow-up herbicide spraying. Injection of herbicide into individual plants has been found to be more precise and effective.

A study in the journal ''Functional Ecology'' also showed that invasive rhododendron nectar was toxic to European honeybees , killing individuals within hours of consumption. It also paralyzed bees of the species ''Andrena carantonica'', 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 was not affected by the rhododendron nectar.

Distribution

The species has two disjunct populations, one in the southwestern Iberian Peninsula and the other near the southern Black Sea Basin . It has also been introduced to Madeira, India, Belgium, England, France and Ireland.

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 forests that covered the peninsula 66 million years ago.

Though it was in Great Britain before the last 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 . In the British Isles, it colonises moorlands, uplands, shady woodlands and in areas of acid soils, often in shaded areas.

Habitat

The species has two disjunct populations, one in the southwestern Iberian Peninsula and the other near the southern Black Sea Basin . It has also been introduced to Madeira, India, Belgium, England, France and Ireland.

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 forests that covered the peninsula 66 million years ago.

Though it was in Great Britain before the last 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 . In the British Isles, it colonises moorlands, uplands, shady woodlands and in areas of acid soils, often in shaded areas.

Uses

''Rhododendron ponticum'' subsp. ''baeticum'' is one of the most extensively cultivated rhododendrons in western Europe. It is used as an ornamental plant in its own right, and more frequently as a rootstock onto which other more attractive rhododendrons are grafted. 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 and bradycardia in humans if consumed in sufficient quantities, due to toxic diterpenes .

In some parts of the world, a controlled dosage of the honey can be taken to induce hallucinations for spiritual or psychological purposes. Such areas include Nepal.