Rhododendron (from the Greek: rhodos, "rose"; dendron, "tree") 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 series. These subgenera can be basically divided into four groups:
* Subgenus Rhododendron: small leaf or lepidotes (with scales on the
underside of their leaves). Type: Rhododendron ferrugineum L.
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 and Sikkim east to Yunnan and Sichuan, with other significant areas of diversity in the mountains of Indo-China, Korea, 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 and New Guinea. 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 national flower of Nepal. It is also the state flower of the US states of Washington and West Virginia, and the state of Sikkim in India.
There are over 25,000 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. All parts of the rhododendron are poisonous to horses, especially the leaves.
The largest natural rhododendron garden in the world is in Bakersville, North Carolina in the USA. The garden is situated on the top of Roan Mountain state park.
One of the largest, if not the largest, collection of cultivated rhododendrons, is in Dunedin, New Zealand, where its temperate climate is well suited. The city hosts an annual Rhododendron Festival (http://www.rhododunedin.com/).
In the UK, the rhododendron is regarded as an ecological pest due to its aggressive growth and displacement of native species.
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