Every azalea is a rhododendron, but botanists took a century to agree
Linnaeus kept azaleas in a genus of their own, telling them apart by counting stamens: five instead of ten. Other botanists grew doubtful, and in 1836 azaleas were folded into Rhododendron. Today they form two subgenera of a sprawling group of roughly 1,000 species, from knee-high shrubs to 30-metre trees.
The name joins the Greek words for rose and tree. Rhododendron is the largest genus in the heath family, with estimates ranging from 850 to 1,200 species, most native to eastern Asia and the Himalaya, with smaller numbers in North America, Europe and Australia. Its range of forms is huge. R. cespitosum of New Guinea may stand just 10 centimetres tall, while R. protistum var. giganteum has been reported at 30 metres, and the leaves of R. sinogrande can exceptionally reach a metre.
Some grow as alpine cushions with tiny flowers; others, in the tropical section Vireya, perch on trees as epiphytes. A species found recently in New Guinea bears blooms up to 15 centimetres wide, the largest in the genus. One of the key dividing lines is microscopic: members of subgenus Rhododendron carry tiny stalked scales, modified hairs, on the undersides of their leaves, a distinction whose importance Koehne recognised in 1893.
Europeans knew the plants long before formal naming. Carolus Clusius described R. hirsutum in the sixteenth century, and Linnaeus established the genus in 1753 with five species. As new finds poured in from Asia during the nineteenth century, classification became a long argument. Isaac Bayley Balfour later sorted species into series, a system that lasted into modern reference works until molecular studies after 2004 forced major rethinking.
Few plants carry so many civic titles. Nepal chose it as its national bloom, the American states of Washington and West Virginia adopted it too, and it holds official status in several Indian states and in provinces of South Korea and China. Most species bloom in bright colours between late winter and early summer.
Source: Rhododendron
