Family Ericaceae > Genus Rhododendron.
As a result of hybridising there are over 10,000 registered varieties of azaleas.
Plant size and form varies from dwarfs, to straggly or compact shrubs up to small trees.
Most are medium-sized shrubs.

Leaves are ommonly from 2.5 to 5 cm long but can be larger.
They are thinner than rhododendron leaves and elliptic to ovate.
The underside has long straight hairs lying almost flat on the surface.

Inflorescences are axillary along the stem as well as terminal.
The calyx has 5 green sepals with pointed tips.

The corolla has 5 (6 – 7) petals that are fused at the base.
It can be funnel-shaped, tubular, bell-shaped or flattish and a few mms up to 12 cm wide.
The single upper petal is the dorsal petal.
The other paired petals are the upper and lower wings.

Colours include white, red, pink and purple.
Only deciduous azaleas have yellow flowers.
There are usually 5 stamens (rhododendrons have 10).

There are many possible variations in the form of the flowers.
In some flowers the sepals are enlarged and the same colour as the petals.

This results in flowers that look as if they have 2 corollas with 10 petals (hose in hose).

Stamens can also be wholly or partially converted into petals.
When only some are converted the resulting petals tend to be small and contorted.
When all are converted the new petals look more like normal ones.
When the calyx and the stamens are converted flowers can have up to 30 or more petals.

The petals can be round to linear, flat or curved backwards and the edge can be
    wavy, twisted or ruffled.

Petals can be the same colour all over, a mix of 2 colours or with stripes, spots or blotches
    in a different colour. All petals, or only the upper one may be marked.
(Rhododendrons can have flushes of another colour or spots on the upper petal.)

All the flowers on a plant can be the same or have different colouring patterns.
The patterns, as well as overall shape can vary from year to year.

Horticulturists divide azaleas into evergreen (that can look like small
    rhododendrons) and deciduous plants.