What is the difference between Rhododendrons and Azaleas ?


By the 1920s, large numbers of species were being introduced to cultivation. A new classification system was devised by Sir Isaac Bayley Balfour (RBGE), though still following the binomial system of Linnaeus where each plant was included within a genus followed by a distinct species name.   Different rhododendron species were grouped into series. 

Further changes, proposed initially by Sleumer in 1949, led to the gradual adoption of a new system in which rhododendrons were grouped into subgenera, sections then subsections. This was as a result of the discovery of new species and increased understanding of the genus. DNA analysis is now allowing other adjustments to be made to their classification. 

This latter system is generally in use today. Plants which are known as azaleas in the horticultural trade are placed within the subgenera Azaleastrum and Pentathera.    None of these have scales i.e. they are elepidote.

Author : Marion Kinns 2024

Footnote: Details on Rhododendron classification can be found on the American Rhododendron Society website.