The variations in flower morphology and flavonol pigment composition in the
petals of Rhododendron kiusianum endemic to Kuju and Aso Mountains and the
ir surrounding areas were investigated.
A typical R kiusianum plant which grows in the Kuju Mountains seems well-ad
apted to severe climatic conditions, such as alpine temperatures and strong
winds, as well as acid soil and the presence of sulfurous acid gas. Althou
gh the species is also distributed at the top of Mt. Yufudake and Aso Mount
ains, the distributional areas of this species are separated from the other
crosscompatible azalea species, such as R. kaempferi, by a summergreen for
est or an open field, respectively. Flower colors of individuals growing on
Mt. Haneyama varied widely, nearly all having prominent blotches on their
petals. The composition of flavonols in their petals also ranged widely. Fr
om these findings, we conclude that the population at Mt. Haneyama seems to
be the result of natural crossing between R. kiusianum and R. kaempferi.