(Rhododendron), any of a genus of woody plants in the heath family (Ericaceae), notable for their attractive flowers and handsome foliage. The genus is large and extremely diverse, comprising about 800 species. They are native chiefly in the North Temperate Zone, especially in the moist acid soil of the Himalayas, southeastern Asia, and the mountains of Malaysia, where they form dense thickets. The genus Rhododendron includes the azalea (q.v.) species, which some gardeners consider distinct.
rhododendron." Encyclopædia Britannica from Encyclopædia Britannica 2007 Ultimate Reference Suite . (2008).
Rhododendrons range in habit from evergreen to deciduous, from low-growing ground covers to tall trees. The first species available for garden use, in the mid-1600s, was R. hirsutum, the hairy alpine rose, which may grow as high as 1 metre (3 feet). Others range from matlike dwarf species only 10 centimetres (4 inches) high (R. prostratum, from Yunnan, China) to trees in excess of 12 m (R. arboreum, R. barbatum, and R. giganteum, from Asia). Leaves are thick and leathery and are evergreen in all but the azalea species, some of which are deciduous. Flowers are usually tubular to funnel-shaped and occur in a wide range of colours—white, yellow, pink, scarlet, purple, and blue.