Rhododendron

Rhododendron is a genus of over 1000 species of woody plants in the heath family, either evergreen or deciduous. Most species have showy flowers. Azaleas make up two subgenera of Rhododendron.

Fire Orange Rhodendendron

 

Species of the genus Rhododendron are native to every continent of the world, except South America and Africa.^[9] The highest species diversity is found in the Himalayas from Uttarakhand, Nepal and Sikkim to Yunnan and Sichuan, with other significant areas of diversity in the mountains of Korea, Japan and Taiwan.

Tropical rhododendron species range from southeast Asia to northern Australia, with 55 known species in Borneo and 164 in New Guinea. Interestingly, the species in New Guinea are native to subalpine moist grasslands at around 3000 metres above sea level in the Central Highlands^{. ]} Relatively fewer species occur in North America and Europe.

Invasive species

Some species (e.g. Rhododendron ponticum in Ireland and the United Kingdom) are invasive as introduced plants, spreading in woodland areas replacing the natural understory. R. ponticum is difficult to eradicate, as its roots can make new shoots.

Insects

A number of insects either target rhododendrons or will opportunistically attack them. Rhododendron borers and various weevils are major pests of rhododendrons, and many caterpillars will preferentially devour them.

Rhododendron species are used as food plants by the larvae of some members of the order Lepidoptera (butterflies and moths) (See List of Lepidoptera that feed on rhododendrons).

Diseases

Main article: List of rhododendron diseases

Major diseases include Phytophthora root rot, stem and twig fungal dieback; Ohio State University Extension provides information on maintaining health of rhododendrons^. Rhododendrons can easily be suffocated by other plants.

Rhododendron is a genus characterized by shrubs and small to (rarely) large trees, the smallest species growing to 10–100 cm (3.9–39 in) tall, and the largest, R. giganteum, reported to over 30 m (98 ft) tall.^[4] The leaves are spirally arranged; leaf size can range from 1–2 cm (0.39–0.79 in) to over 50 cm (20 in), exceptionally 100 cm (39 in) in R. sinogrande. They may be either evergreen or deciduous. In some species, the undersides of the leaves are covered with scales (lepidote) or hairs (indumentum). Some of the best known species are noted for their many clusters of large flowers. There are alpine species with small flowers and small leaves, and tropical species such as section Vireya that often grow as epiphytes. Species in this genus may be part of the heath complex in oak-heath forests in eastern North America.