Seed flavonoids of the Podalyrieae and Liparieae (Fabaceae)

A study of the phenolic compounds of the closely related papilionoid tribes, Podalyrieae and Liparieae, proved that the flavonoid patterns of hydrolysed seed extracts are remarkably conservative. Butin (7, 3', 4'-trihydroxyflavanone), 3'-hydroxydaidzein (7, 3', 4'-trihydroxyisoflavone), vicenin-2 (6, 8-di-β-D-glucopyranosyl-5, 7, 4'-trihydroxyflavone) and orobol (5, 7, 3', 4'-tetrahydroxyisoflavone) were isolated and identified as the major flavonoids. The seeds of Amphithalea, Coelidium, Liparia, Xiphotheca, Calpurnia, Stirtonanthus and Podalyria accumulated three isoflavone O-glycosides that yielded 3'-hydroxydaidzein on hydrolysis. In contrast, Virgilia contained a unique combination of vicenin-2 and orobol. Vicenin-2 was also present in Calpurnia as a major compound, but Stirtonanthus insignis was the only other species studied that contained orobol (in trace amounts only). Butein, a chalcone, was reported by Harborne from the seed of Cyclopia subternata. This compound's flavanone analog, butin, was the principal component in Cyclopia. A cladistic analysis, using flavonoid, alkaloid and morphological data, showed that the seed flavonoids of the Podalyrieae and Liparieae behave rather poorly as cladistic characters. They are, however, of considerable taxonomic value at the tribal level favouring the opinion that the two tribes should be combined. The apparent absence of flavonoids in the seed of Hypocalyptus supports the suggestion that it should be excluded from the Liparieae. Flavonoids also show that the Argyrolobium-group is very different from the tribe Crotalarieae and support the recent transfer of this group to the tribe Genisteae.