Comparative biochemistry of the flavonoids—VII : Correlations between flavonoid pigmentation and systematics in the family primulaceae

Abstract

A survey of the flavonoids and other phenolics in leaf and flower of a hundred species, representing 18 of the 25 genera, of the Primulaceae has shown that the richest variation in pigment structures occurs in the genus Primula. Thus, the rare 7- O-methylated anthocyanin hirsutin is confined to this genus (in 30 of 41 cyanic species) and occurs in all subgenera except Auganthus, where it is replaced by malvin or malvidin 3-glucoside as the principal petal pigment. The related rosinin, earlier detected in P. rosea petals, has now been found in P. clarkei in the same section. Peonidin is only found as a principal pigment in the crimson calyces of P. viali. Cyanin and other cyanidin glycosides are confined to the petals of P. chungensis, P. aurantiaca, P. cockburniana (all section Candelabra) and P. warshenewskiana (section Farinosae). Delphinidin occurs as the principal petal pigment only in P. ioessa. Other genera of the family ( Cortusa, Dodecatheon, Cyclamen, Soldanella) have anthocyanins based on malvidin, delphinidin or cyanidin. The yellow flavonol in petals of P. vulgaris, P. veris and P. elatior (all section Vernales) previously reported as quercetagetin has now been found to be the 8-hydroxy isomer, gossypetin. Gossypetin also occurs in yellow petals of four species of the section Sikkimenses, and in one of these, P. alpicola, it is accompanied by herbacetin. Gossypetin has also been detected in two closely related genera Dionysia and Douglasia but yellow flower colour elsewhere in the family (e.g. Lysimachia) is probably carotenoid. The simple 3′,4′-dihydroxyflavone, identified in this family for the first time as a leaf glucoside, is of biogenetic interest in relation to the production of flavone in the leaf farina of Primula. It is also of systematic interest, since it occurs widely in Primula (in 39 of 55 species) and in three related genera ( Cortusa, Dodecatheon and Dionysia) in the subfamily Primuleae but was not otherwise detected in the family. Other new phenols of taxonomic interest in Primula include a new trihydroxyflavone and a substance, chionanthin, with a distinctive pink fluorescence in u.v. light, which is possibly related to 7-hydroxyflavone. Leucocyanidin, leucodelphinidin, kaempferol and quercetin occur throughout the family. By contrast, myricetin is uncommon (in 4 Primula and in 2 Lysimachia spp.) and the flavones apigenin and luteolin have only been detected so far in Soldanella, presumably a phyletically advanced taxon. Kaempferol and quercetin occur in Primula leaf and petal in combination with a range of sugars and the distribution of some of these glycosides is clearly related to classification at the subgeneric level. The very common kaempferol 3-gentiotrioside, thus, is rare in section Candelabra and absent from Sikkimenses (both subgenus Aleurita), being largely replaced by rutin, which in turn is rare in the subgenus Auganthus and absent from the subgenus Craibia.