Fig. 2.

Rhododendron smirnowii (subgenus Hymenanthes; pink flowers) and R. luteum (subgenus Pentanthera; yellow flowers) growing together in the Pontus mountains on the Black Sea coast of Turkey, part of the SW Eurasia refugial region. Both these subgenera have independently developed Tertiary relict distributions, with species in SW Eurasia, south-eastern and western N America, and Japan (Kron, 1993; Milne, 2004). Subgenus Hymenanthes additionally has species in other parts of E Asia, most notably the Himalayas where rapid radiation appears to have occurred (Milne, 2004).