A flavonoid survey of Fraxinus (Oleaceae) in eastern Asia, and the overlooked species Fraxinus hopeiensis T. Tang in northern China

Abstract

From a survey of 14 flavonoids of 19 Asian taxa of Fraxinus, flavonols were present in most taxa of sects. Ornus, Fraxinus, and Sciadanthus, while flavones were only detected in Fraxinus lanuginosa in Japan and Fraxinus hopeiensis in China of sect. Ornus and Fraxinus chiisanensis in Korea (as incertae sedia sensu Wallander). The present data failed to clearly distinguish many taxa within the genus because of the extreme monotony of flavonoid content. However, the dichotomy on a smaller scale was observed in Fraxinus, where this chemical approach was useful in the determination of natural groupings of the overlooked taxon F. hopeiensis in China, F. lanuginosa in Japan, and F. chiisanensis in Korea. The gain of O-flavone appears to be a significant evolutionary step; however, the sporadic occurrence of O-flavone in some species is the result of chemical advancement. The present study demonstrated that flavonoid chemistry may indeed be as variable as the morphological features, with no significant flavonoid differences observed at the species level. However, F. hopeiensis, found in the mountain regions of Hebei in northern China, has petals like Fraxinus sieboldiana and F. lanuginosa and is clearly different from other related taxa, including Fraxinus rhynchophylla and Fraxinus chinensis. This study shows that F. hopeiensis is morphologically, chemically, and geographically distinct and should be treated as a distinct species.