About

Rhododendron (; pl.: rhododendra), from Ancient Greek ῥόδον (rhódon), meaning "rose", and δένδρον (déndron), meaning "tree", is a very large genus of about 1,024 species of woody plants in the heath family (Ericaceae). They can be either evergreen or deciduous. Most species are native to eastern Asia and the Himalayan region, but smaller numbers occur elsewhere in Asia, and in North America, Europe and Australia.

Various species of Rhododendron are the national flower of Nepal, the state flower of Washington and West Virginia in the United States, the state flower of Nagaland and Himachal Pradesh in India, the provincial flower of Jeju Province in South Korea and Jiangxi in China, and the state tree of Sikkim and Uttarakhand in India. Most species have brightly coloured flowers which bloom from late winter through to early summer.

How to grow it

Both species and hybrid rhododendrons (including azaleas) are used extensively as ornamental plants in landscaping in many parts of the world, including both temperate and subtemperate regions. Many species and cultivars are grown commercially for the nursery trade.

Rhododendrons can be propagated by air layering or stem cuttings. They can self-propagate by sending up shoots from the roots. Sometimes an attached branch that has drooped to the ground will root in damp mulch and the resulting rooted plant then can be cut off the parent rhododendron. They can also be reproduced by seed dispersal or by horticulturalists collecting the spent flower buds and saving and drying the seed for later germination and planting.

Safety

Some species of rhododendron are poisonous to grazing animals because of a toxin called grayanotoxin in their pollen and nectar. People have been known to become ill from eating mad honey made by bees feeding on rhododendron and azalea flowers. Xenophon described the odd behaviour of Greek soldiers after having consumed honey in a village surrounded by Rhododendron ponticum during the march of the Ten Thousand in 401 BCE. Pompey's soldiers reportedly suffered lethal casualties following the consumption of mad honey that was deliberately left behind by Pontic forces in 67 BCE during the Third Mithridatic War. Later, it was recognized that honey resulting from these plants has a slightly hallucinogenic and laxative effect. The suspect rhododendrons are Rhododendron ponticum and Rhododendron luteum (formerly Azalea pontica), both found in northern Asia Minor. Eleven similar cases during the 1980s have been documented in Istanbul, Turkey.

Where it grows

Species of the genus Rhododendron are widely distributed between latitudes 80°N and 20°S and are native to areas from North America to Europe, Russia, and Asia, and from Greenland to Queensland, Australia and the Solomon Islands. The centres of diversity are in the Himalayas and Maritime Southeast Asia, with the greatest species diversity in the Sino-Himalayan region, Southwest China and northern Burma, from India – Himachal Pradesh, Uttarakhand, Sikkim and Nagaland to Nepal, northwestern Yunnan and western Sichuan and southeastern Tibet. Other significant areas of diversity are in the mountains of Korea, Japan and Taiwan. More than 90% of Rhododendron sensu Chamberlain belong to the Asian subgenera Rhododendron, Hymenanthes and section Tsutsusi. Of the first two of these, the species are predominantly found in the area of the Himalayas and Southwest China (Sino-Himalayan Region).

Uses

Rhododendron species have long been used in traditional medicine.

Other Rhododendron plants

Rhododendron album · Rhododendron anthopogon · Rhododendron argyrophyllum · Rhododendron augustinii · Rhododendron bureavii · Rhododendron calophytum · Rhododendron calostrotum · Bell Flowered Rhododendron · Bent-style rhododendron · Rhodora · Catawba rosebay · Georgian Snow Rose