Flavonoid chemistry ofWeigela (Caprifoliaceae) in Korea

Fifteen flavonoids were isolated from flowers and leaves of four species ofWeigela [W. florida (Bunge) A. DC.,W. praecox (Lemoine) Bailey,W. hortensis (Sieb. et Zucc.) K. Koch, andW. subsessilis (Nakai) Bailey] of Korea and one species (W. coraeensis Thunb.) of Japan. The flavonoid data indicated the presence of two distinct chemical groups: the “yellow flower” type producing flavonols and the “red flower” type producing flavonols and flavones. Two cyanidin 3-O-glycosides (glucoside and glucose-xylose) also occurred in all examined taxa. In the floral color-changing species,W. subsessilis, only quercetin glycosides predominated in floral tissue at first, decreasing in number and quantity with time. Instead, cyanidin 3-O-glycosides became present predominantly in flower color changing tissue from yellow to mauve.Weigela florida produced apigenin and luteolin glycosides, along with cyanidin 3-O-glycosides, which were also found inW. subsessilis. Within a relatively limited number of individuals (five),W. hortensis was unique in its production of all flavonols, flavones, and anthocyanins, although two individuals lacked flavone compounds but possessed all flavonols and anthocyanins. In effect, the putative hybrid,W. hortensis of Korea showed additive profiles of the parental marker compounds ofW. subsessilis andW. florida. Pollinator (andrenid bees) non-discrimination betweenWeigela flower-color morphs leading to non-assortive mating was a common, which indicated no breeding barrier among species. This flavonoid study indicated that species of both sections,Weigela andCalysphyrum appeared in each chemical grouping and it was obvious that the arrangement based on flavonoids cut across the sectional treatment of Hara. Floral tissues may be directly involved in the evolutionary strategy of pollination mechanisms and hence, their inherent flavonoids may no longer support taxonomic relationships. The presence of flavone glycosides inWeigela would support that tribe Dievilleae have a closer affinity to tribe Lonicereae within the Family Caprifoliaceae.