Abstract
The variations in pigments and morphological characteristics among flowers of Rhododendron kiusianum and R. kaempferi endemic to the Unzen mountain mass were investigated.The typical R. kiusianum has small, exclusively purple and almost blotchless flowersgrows at the higher elevation of this mountain mass. Some members of this species growat relatively lower elevations near hot springs, which we attribute to its environmentaladaptations to acid soil and the presence of sulfurous acid gas. A high ratio of 5-methylated flavonols to total flavonol content occurs in the petals of this species.Contrarily, azaleas distributed on the mid-elevations of this mountain have wide phenotypic variation with respect to flower color and size. Many individuals with prominentblotches on their petals may be natural hybrid progenies between R. kiusianum and R.kaempferi. We base this supposition on the various flavonol constituents in the petals.The hybrid population from Mt. Kusenbudake and Mt. Azumadake apparently resultedfrom the introgression of R. kaempferi which seems to be a consequence of an ecologicalsuccession following volcanic activities.
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