"Rhododendron" is a genus of shrubs and small to (rarely) large trees, the smallest species growing to tall, and the largest, "R. protistum" var. "giganteum", reported to tall. The leaves are spirally arranged; leaf size can range from to over , exceptionally 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.