Although Betula is a small genus of ca. 60 species in the world, relatively little systematic work has been done on Asian birch, apparently due to the difficulties of working with wide distributed taxa in China, Korea, Rusia and Japan. Seventeen flavonoids were isolated from the leaves of seven Korean birch taxa, representing one section (Betula) and four subsections (Costatae, Chinenses, Betula, and Davuricae) according to Kuang and Li`s classification. Two chemical groups were evident : one producing only flavonols, and a second producing flavonols and flavones. These two chemical groups did not correspond to any of the sectional groups based on morphology. The flavonoid data supported the hypothesis that sect. Betula, subsect. Costatae originated from the ancestor of Betula. Also, by combining existing flavonoid data, it is possible to develop a phylogenetic scheme illustrating the relationship between sect. Betulaster and subsects. Betula and Fruticosae including subsect. Davuricae of sect. Betula. Flavonoid chemistry supported the treatments of subsects. Costatae and Chinense as a unified group rather than as two different subsections and further favored the elevation of subsections of sect. Betula to all sectional rank including sect. Betulaster (sensu Kuang and Li).
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