There are, in fact, deciduous Rhododendrons and evergreen Azaleas. In botanical terms, the flowers of typical Rhododendrons mostly have ten stamens while Azaleas generally have five, but even this difference is not hard and fast. Generally, the elepidotes are the 'standard' Rhododendrons with large leaves and flowers while the lepidotes are the so-called 'dwarf' Rhododendrons with small leaves and flowers. Again, the botanical difference is that the lepidotes have small to microscopic scales on the undersurface of their leaves while the leaves of the elepidotes are entirely scale-less. The deciduous or 'standard' Azaleas are large, upright shrubs with relatively large trusses.
Popular colours are yellow and orange, but they are available in every colour except blue.
Flowers are produced individually or in small clusters. Their colour range is more restricted as they are not available in blue or yellow. Finally, there are another group of Rhododendrons that hail from the sub-tropics and tropics of the East Indies. They are called Vireya Rhododendrons. Within Atlantic Canada, we can only grow them as houseplants.