Petal flavonoid compositions of 39 tree peony cultivars from Xibei (northwest China) were investigated in order to study the chemotaxonomic relationship among tree peony species. Six anthocyanins, the 3-O-glucosides and 3,5-di-O-glucosides of three anthocyanidins-pelargonidin (Pg), cyanidin (Cy), and peonidin (Pn)-exist in petals without a blotch at the base. The flowers are classified into three anthocyanidin phenotypes: "Pn, Pg > Cy"; "Pn, Cy"; and "Pn, Cy > Pg". Furthermore, the yellow pigments are identified as three flavones and three flavonols: apigenin, luteolin, chrysoeriol, and kaempferol, quercetin, and isorhamnetin, respectively. Ward's minimum-variance cluster analysis with principal component analysis produced a dendrogram using standardized scores of 20 pigment variables. Of 39 cultivars, 11 clustered with white flowered Paeonia rockii and 17 with pink flowered P rockii. The other 11 cultivars matched either P. delavayi or P. potaninii. The result suggests that the Xibei tree peony originated mainly from P rockii.
