Rhododendrons are most closely related to heathers (Calluna,
Erica) and heaths (Phyllodoce, etc.). The genus Rhododendron
is very large containing more than 900 different species! Within this
huge group are four commonly recognized subgroups. Three of these subgroups
are distinguished by the hairs found on the leaves and other parts of
the plant. Members of the lepidote group possess unique scale-like hairs
and members of the elepidote group lack the scale hairs, but have elaborately
branched hairs instead.The Tsutsusi group contains the evergreen azaleas.
This group can be indentified by flattened, rusty or brown-colored hairs
on the leaves and stems. Deciduous azaleas belong to the Pentanthera group.