Flavonoid Variation in Hawaiian Bidens

Abstract

The 19 species and 8 subspecies of Bidens endemic to the Hawaiian Islands are mor- phologically and ecologically diverse, yet all are the result of adaptive radiation from a single ancestral immigrant species. They accumulate a rich array of flavonoids, with chalcone (butein and okanin) and aurone (sulfuretin and maritimetin) derivatives, including mono-, di-, and triacetylated glucosides, making up the bulk of the profile. A flavanone (eriodictyol), three flavones (apigenin, luteolin and diosmetin), and two flavonols (kaempferol and quercetin), in various glycosylated forms, were also found. Butein 4-methyl ether and di-, tri-, and tetra-O-methyl derivatives of okanin occurred in a few taxa. This flavonoid chemistry is typical of other non-Hawaiian species of Bidens that have been investigated. In general, variation within single populations was as great as differ- entiation among taxa. Colonization and adaptive radiation on the Hawaiian Islands have not resulted in significant differentiation from continental species of Bidens in flavonoid chemistry. Despite considerable genetic variability for flavonoids in Hawaiian Bidens, adaptive radiation and speciation on the Islands have not resulted in differentiation among species for flavonoids.