Comparative biochemistry of the flavonoids-IV. : Correlations between chemistry, pollen morphology and systematics in the family plumbaginaceae

Abstract

Fifty-five species, representing ten of the eleven genera of the family Plumbaginaceae have been surveyed for flavonoids and other phenolic constituents in root, leaf and flower. The results reveal a close correlation between chemistry, pollen morphology and taxonomy. The most useful chemical “marker” is 5-hydroxy-2-methyl-naphthoquinone (plumbagin) which occurs in roots of all ten taxa examined of the tribe Plumbagineae (plants with monomorphic pollen) and which is uniformly absent (0 out of 44 species) from plants of the tribe Staticeae (with dimorphic pollen). There are also characteristic differences between the tribes in their flavonoid pigments. Thus, all but two of the Plumbago and Ceratostigma species studied contain one or other of five rare O-methylated flavonoids, namely azaleatin, 5- O-methylmyricetin, capensinidin, pulchellidin and europinidin. The two latter pigments are new anthocyanidins, provisionally identified as 5- O-monomethyl and 5,3′-di- O-methyldelphinidin. In addition, Plumbago europea leaf contains a new flavonol 7- O-methylmyricetin (europetin), a substance which forms a link between the Plumbaginaceae and a neighbouring family, the Primulaceae. Of the seven Plumbago species examined, P. rosea is the most distinctive, for besides lacking 5- O-methylated flavonols, it contains in its flowers a mono- and a digalloylglucose. The anthocyanidins in the Plumbagineae occur as 3-rhamnosides, 3-galactosides or 3-glucosides. By contrast, in the tribe Staticeae, the main anthocyanins are malvidin 3,5-diglucoside ( Armeria spp.) and petunidin 3-rhamnoside-5-glucoside (most Limonium spp.). Members of the Staticeae characteristically have large amounts of myricetin glycosides in the leaves. Examination of the most primitive member of the Staticeae, Aegialitis annulata, which is anomalous in having monomorphic (instead of dimorphic) pollen, showed it to be unusual chemically. The main leaf flavonoids were 3- O-methyl ethers of quercetin and myricetin; the latter is a new pigment, annulatin. The absence of plumbagin and 5- O-methylated flavonols from this plant indicates that it has been correctly placed, in spite of its pollen morphology, in the Staticeae.