Chemical Contributions to Taxonomy and Phylogeny in the Genus Artemisia

The sesquiterpenic lactones of the family Compositae represent a group of compounds that appear to be of common origin and formed by closely allied biosynthetic processes. They provide an attractive means for further assessing the potential value of chemical characters in chemosystematics, and for examining presently accepted classifications within the family. The genus Arternisia, which is divided into several morphologically differentiated sections, provides a unified group of plants for such a study and is reviewed with respect to the present state of the chemistry of its lactonic constituents. The results of recent studies in the author's laboratory, along with those of others, are considered in detail with regard to what the chemical constituents reveal in respect to the taxonomy and phylogeny of the genus. Related genera are discussed in the same context. INTRODUCTION The tribe Anthemideae of the family Compositac includes about sixty genera and over nine hundred species. The largest and most widely distributed of these is the genus Artemisia, comprising some four hundred species'. Because of the applications of Artemisia in the practice of folk medicine (infusions for various gastrointestinal and haemorrhagic disorders; moxibustion); the use of A. absinthium as the source of a widely used bitter flavouring principle (wermut, or wormwood; vermouth, absinthe); and the early use of santonin as an important vermifuge, this genus has been the subject of many chemical investigations for over a century. Much of the earlier study was directed to a search for new sources of santonin, with the result that this compound is known as a constituent of about twenty species of Artemisia2. Recent years have seen an expansion of studies of Artemisia as a part of an increasing interest in the chemistry of plants of the Compositae, principally with respect to the sesquiterpene lactones, a class of compounds almost unique to this family3. The compositae comprise about 20 000 species4, usually divided into about thirteen tribes. Some 170 sesquiterpene lactones are now known in the family, derived in largest part from six tribes: Helenieae, Inuleae, Ambrosieae, Anthemideae, Cynareae and Senecioneae. Although the chemical investigations that have been carried out to the present time embrace less than one per cent of the known species of the family, certain chemotaxonomic hypotheses appear to be taking form from these studies.