Rhododendron is a genus of flowering plants in the family Ericaceae. This is such a large genus that the plants are organised by subgenus, section, subsection and alliance.
These subgenera can be basically divided into four groups:
- large leaf or elepidotes (without scales on the underside of their leaves)
- small leaf or lepidotes (with scales on the underside of their leaves)
- evergreen azaleas
- deciduous azaleas.
Rhododendron is a very widely distributed genus, but a major concentration of diversity occurs in the Sino-Himalayan mountains of southeast Asia from central Nepal east to Yunnan and Sichuan, with other significant areas of diversity in the mountains of Indo-China, Japan and Taiwan. Several species also occur in North America and a few in Europe, and some tropical species occur as far south as Borneo. They grow well in acid soil, and are noted for their many clusters of large trumpet-shaped blooms and their glossy oval leaves. Most rhododendrons flower for only a brief period each year, but during that time they provide a stunning display of massed colour.
The Rhododendron is the State Flower of Washington and West Virginia.
There are several hundred cultivars of Rhododendron. These have been bred to have larger or smaller flowers, and a vast array of petal colours. An example of a cultivar popular in the US is Rhododendron 'President Roosevelt'.
Rhododendrons have a toxin called grayanotoxin in their pollen and nectar. People have been known to become ill from eating honey made by bees feeding on rhododendron and azalea flowers.
See also: azalea
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