Fungitoxic dihydrofuranoisoflavones and related compounds in white lupin, Lupinus albus

Isoflavonoids produced by Iris pseudacorus leaves treated with cupric chloride

This review is concerned with variation of flavonoid patterns within species. Many examples of species with invariant flavonoid patterns are known; there are at least as many examples where complex arrays of pigments are known. Eight categories of variation are discussed: 1) qualitatively invariant pigment profiles, 2) quantitative variation, 3) flavonoid races that do not correspond to recognized taxonomic groups, 4) flavonoid races that do correspond to recognized taxonomic groups, 5) flavonoid profile differences between different ploidy levels, 6) differences between organs or between tissues, 7) differences between developmental stages, and 8) environmentally influenced flavonoid profiles. These types of variation seem to occur randomly in the plant kingdom. Members of the same family, or in some cases, the same genus, can display different types of variation. Careful attention to these sources of variation is necessary before flavonoid characters can be used in taxonomic studies.

Intraspecific flavonoid variation

Modern plant biochemical systematics represents an interdisciplinary approach to the many problems of plant classification and can be dated from 1962, the year in which the first international conference on this topic was held. From the proceedings of this meeting, which were published in the following year (Swain, 1963), it is clear that flavonoids were already regarded as potentially important taxonomic markers since no less than a third of the 18 chapters which made up the volume dealt inter alia with these constituents. In addition, one of the very first examples of a significant correlation between chemistry and taxonomy was the discovery of a relationship between sectional classification and flavonoid heartwood constituents in the genus Pinus (Erdtman, 1963).

The Biochemical Systematics of Flavonoids

This review is mainly concerned with the structures, sources and biological properties of those natural products containing the 1,2-diphenyl-propane ring system (see Chart 1, and compare with the isomeric 1,3-diphenylpropane skeleton common to flavonoid compounds), and which collectively are known as isoflavonoids. Also briefly considered, however, are the glucosidic deoxybenzoin derivative, onospin (630), as well as several 2-arylbenzofurans (Table 2, Section R) of leguminous origin which lack a carbon atom corresponding to that marked (Chart 1) with an asterisk (*). These latter compounds and onospin are included because whilst they cannot be regarded as isoflavonoids, it is by no means uncommon to find that in the family Leguminosae they co-occur with (and in certain instances may originate from) isoflavonoids having similar aromatic substitution.

William A. Dement

Papers

Flavonoids of north american species of Thermopsis