Rhododendron ponticum, called common rhododendron or pontic rhododendron, is a species of Rhododendron native to southern Europe and southwest Asia.
Description
R. ponticum is a dense, suckering shrub or small tree growing to tall, rarely. The leaves are evergreen, long and wide. The flowers are in diameter, violet-purple, often with small greenish-yellow spots or streaks. The fruit is a dry capsule long, containing numerous small seeds. The two subspecies are:
evidence shows it had a much wider range across most of southern and western Europe before the Late Glacial Maximum, or until about 20,000 years ago. It was noted by the botanist Joseph Pitton de Tournefort during his travels in the Near East in 1700–02, and so received its name from Linnaeus to identify the ancient kingdom on the south shores of the Black Sea, Pontus, in which it grew. At the other end of its range, in southern Spain, Linnaeus' friend and correspondent Clas Alströmer found it growing with oleander. It was introduced to Britain as an ornamental shrub in 1763, and later planted as cover for game birds. It is now considered to be an invasive species.
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 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.
Invasive species
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.
