The Asteraceae is characterized by structurally diverse sesquiterpene lactones and furanosesquiterpenes. In this review the tribal, subtribal and generic distribution of sesquiterpene lactones is examined and the compounds’ utility as taxonomic characters discussed. Sesquiterpene lactones fulfill the major requirements for good analytic and synthetic characters. Studies of infraspecific sesquiterpene lactone variation indicate that different elements within complex taxa are often defined by distinct chemistries, termed chemotypes. Chemotypes have been identified within many of the thoroughly investigated taxa:Ambrosia camphorata, A. chamissonis, A. confertiflora, theA. cumanensis-A. psilostachya-A. artemisiifolia complex,A. dumosa, Artemisia tridentata, Gaillardia pulchella andMelampodium leucanthum. Such an analytic usage is mostly restricted to the infraspecific level. Synthetic usage at the interspecific level and above profits from the application of a biogenetically based methodology for sorting out the complex molecules’ carbon-skeletal and substitutional features into unit characters. Cladistics or Hennigian phylogenetic systematics provides a useful framework for such an analysis. Preliminary surveys indicate that sesquiterpene lactones are especially good characters for differentiating subtribes within several major tribes: the Vernonieae, Heliantheae and Mutisieae. As yet, too few data are available for other tribes to discern such patterns. Species surveys inVernonia, Ambrosia, Iva, Parthenium,Tetragonotheca andArtemisia demonstrate that sesquiterpene lactones are useful in discerning infrageneric groups. The biogenetic cladistic analysis of the interspecific sesquiterpene lactone variation inIva shows the efficacy of this analytical methodology. At present, such biogenetically based approaches are impeded by limited biosynthetic evidence and the erratic distribution of sesquiterpene lactones within the family. Instances of apparent displacement of sesquiterpene lactones by other terpenoids (i.e. sesquiterpene furans, alcohols and acids, diterpenes, diterpene acids, etc.) at various taxonomic levels suggest that ultimately sesquiterpene lactones must be interpreted as taxonomic characters in the context of the family’s total terpene chemistry. All taxa from which sesquiterpene lactones have been reported are listed together with the compound names, major structural features and the literature cited. A less-complete listing is provided for taxa producing furanosesquiterpenes. Structures for all reported compounds are included. Two appendices listing alphabetically taxa and compounds and relevant text page numbers permit cross-indexing of plants and compounds.

Sesquiterpene lactones as taxonomic characters in the asteraceae

Field work in Paraguay, Peru, Colombia and Mexico, including field organoleptic tests and interviews, was carried out in search of sweet-tasting Stevia species. Results of such tests performed on at least 31 species, as well as ethnobotanical data on 9 species, are presented. The data obtained showed that leaves of no other Stevia species studied possessed a potent sweet taste comparable to that of S. rebaudiana leaves. Since only 15% of the approximately 200 known species in this genus were investigated in this study, it is quite possible that further research may reveal additional sweet-tasting Stevia species.

Potential sweetening agents of plant origin. II. field search for sweet-tasting Stevia species

Stevia rebaudiana is a remarkable South American plant that has become widely used in certain parts of the world as a natural sweetening agent and dietary supplement. Purified extracts of S. rebaudiana have been used as sweeteners and flavor enhancers in the food industry in Japan for over a quarter of a century, and have been found to be up to 300 times sweeter than sucrose.This comprehensive volume provides reviews on the botany, ethnobotany, and chemical constituents of the genus Stevia and examines the chemical synthesis of such compounds as steviol and stevioside. The perceived safety of these compounds has become somewhat controversial in recent years, and a thorough consideration of the pharmacology and biological activity is provided. The final two chapters offer some insight into the various applications of S. rebaudiana extracts and stevioside in Japan and Korea, the two countries with the most extensive use of these food additives at present.Containing numerous up to date references, the book will appeal to a wide segment of the scientific community at all levels, especially those in the fields of natural products, pharmacy, pharmacognosy, plant science, agriculture and the food and beverages industry.

Lakshmi N. Dutta

Papers

Zwei neue guajanolide sowie weitere longipinenester aus Stevia-arten