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Species - Rhododendron


Recognised by the IUCN SSC Invasive Species Specialist Group as a pest plant.


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Rhododendron (Rhododendron ponticum)

A species of Rhododendron native to southern Europe and Asia as far east as China. Thrives in milder, wet climates and poor, acidic soils. Fossil evidence suggests a wider range across southern and western Europe up to 20,000 years ago. R ponticum subsp baeticum is one of the most extensively cultivated rhododendrons in western Europe today. Introduced to the UK in about 1760s, it became widely distributed by the commercial nursery trade in the late i8th and early 19th centuries. Now widespread as an ornamental plant in its own right but more frequently as a rootstock on to which other more attractive rhododendrons are grafted.

In form a dense, suckering shrub or small tree growing to 5 m tall, rarely 8 m. The waxy leaves are evergreen, 6 to 18 cm long, 2 to 5 cm broad. Flowers appear in May and June, 3.5 to 5 cm in diameter, violet-purple, often with small greenish-yellow spots or streaks. The fruit is a dry capsule 15 to 25 mm long, containing numerous tiny seeds that are wind dispersed.  Each flower head can produce between 3 and 7 thousand seeds; thus, a large bush can produce several million seeds per year. The roots readily send up suckers from below the graft, often enabling it to overtake the intended grafted rhododendron.

Honey produced from this plant is reputed to be poisonous to humans if consumed in sufficient quantities — a belief that goes back to the 4th century BC. The symptoms are intestinal and cardiac problems but they are normally short-lived and rarely fatal.

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