Rhododendrons are divided into four main groups:

• small-leaf = scaly-leaf = lepidote rhododendrons
• large-leaf = non-scaly-leaf = elepidote rhododendrons
• evergreen azaleas
• deciduous azaleas

By convention, species names are shown in lower case, such as R. maximum, while hybrid names are shown with initial capital letters and enclosed in single quotes, such as R. 'Millie Mac'.