There seem to be multiple plural forms of rhododendron:
rhododendra (seems to be a British form but probably the correct form)
while the plural of azalea is always azaleas.
My impression is that rhododendron (or rhododendra) refers to members
of the genus Rhododendron and rhododendrons refers to rhododendron
For example rhododendron (or rhododendra) are Ericaceous and that
includes azaleas. [or] R. occidentale and R. viscosum are native
American rhododendron (or rhododendra) and are deciduous azaleas.
And there are pink rhododendrons growing next to the azaleas. [or]
America and Nova Zembla are popular East Coast rhodendrons.
I tend to think that rhododendron (or rhododendra) is the plural form
for the members of the genus rhododendron and hence a taxonomic term;
and that rhododendrons are rhododendron plants and hence a
The distinction isn't always followed in books. Can anyone elaborate?