Our naturalised Rhododendrons, conventionally recorded as R. ponticum, are a hybrid swarm from four species of the Ponticum group: R. ponticum L. ss. (Portugal, Spain, Bulgaria, Turkey, Georgia and Lebanon); R. catawbiense Michx. (eastern North America); R. maximum L. (eastern North America) and R. macrophyllum G. Don (western North America).

R. ponticum ss. is a frost-tender, unassuming and shy-flowering shrub, quite unlike our blousy invasive plant. These are a complex mix of similar hybrids which functions as a species, and is apparently endemic to Britain and Ireland.

A key to the four species is given, but most plants will be a mixture, although individual characters may often be taken to imply something of the parentage.