Systematic aspects of foliar flavonoids in subsect. Carpinus (Carpinus, Betulaceae)

Foliar flavonoids from nine taxa of subsection Carpinus (Carpinus, Betulaceae) were examined. A total of 10 compounds were isolated and identified, mainly mono- and di-glycosides of flavones (apigenin and luteolin) and/or flavonols (myricetin, kaempferol and quercetin). By comparing the results of flavonoid chemistry with the morphological characteristics and geographic distribution patterns, subsection Carpinus might be differentiated into two ancestor-based groups, one consisting of Carpinus tientaiensis, Carpinus londoniana, and Carpinus betulus, the other Carpinus viminea var. viminea, C. viminea var. chiukiangensis, Carpinus laxiflora, and Carpinus caroliniana. A major trend in the reduction of the number of compounds from the primitive to the advanced was observed in subsect. Carpinus, and the chemical simplification seems to be related to species differentiation within the subsection. The presence of isoflavones in C. laxiflora and C. caroliniana revealed their advancement chemically, but C. betulus and C. londoniana showed no chemical differentiation. Overall intercontinental divergence of Carpinus was not confirmed by this study. A number of infraspecific taxa in the subsect. Carpinus were chemically identical with their original varieties except the C. viminea complex. This might be because sect. Carpinus is undergoing slower radiation; significant biochemical differentiation among infraspecific taxa seems not to have occurred yet. These flavonoid data reflected intrasectional parallelisms and intersectional radiation in Carpinus.