. Biochemical systematics. Biochemical variation; Botany. O^HaC 0 HsCqp^ H2C helenalin Herz and his coworkers (Herz et ah, 1960; Herz £ind Hogenaur, 1962) have been investigating certain Helenium species along with species of several related genera. Sesquiterpene lactones of the helenalin type occur in all three sections of Helenium (Table 13-5) as well as a number of other genera. Helenalin is found in Actinospermum also, and though helenalin itself has not been found in Balduina, a related substance, balduilin, is present in this genus. The close morphological similarity between Actinospermu
. Biochemical systematics. Biochemical variation; Botany. O^HaC 0 HsCqp^ H2C helenalin Herz and his coworkers (Herz et ah, 1960; Herz £ind Hogenaur, 1962) have been investigating certain Helenium species along with species of several related genera. Sesquiterpene lactones of the helenalin type occur in all three sections of Helenium (Table 13-5) as well as a number of other genera. Helenalin is found in Actinospermum also, and though helenalin itself has not been found in Balduina, a related substance, balduilin, is present in this genus. The close morphological similarity between Actinospermum and Balduina indicates that the presence of these similar sesquiterpenes is not coincidental. Helenium is placed in the tribe Helenieae while Actinospermum and Balduina are both placed in the tribe Helian- theae mainly on the basis of technical features of the capitulum. However, Rock (1957) has independently suggested (on morphological grounds) that the three genera are closely related, an interpretation which is supported by this sesquiterpene chemistry. However, sesqui- terpenes also occur in a number of other genera of the family Com- positae, including Artemisia, Inula, Iva, Ambrosia, Parthenium, and Balsamorhiza. Artemisia belongs to the tribe Anthemideae and Inula to the tribe Inuleae, while the last four genera are placed in the tribe Heliantheae. Before discussing the characteristic sesquiterpenes of the various tribes it is pertinent to note that a number of lower terpenes are found in the tribe Anthemideae, especially in Artemisia species: 1,8-cineole {Artemisia); 1-camphor {Artemisia, Achillea); fenchol {Artemisia); and thujon {Tanacetum) (Karrer, 1958). * The structure of tenulin is modified to conform more closely to inferences de- rived from the revised formula of isotenulin, helenalin, and balduilin (Herz et al, 1961).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and a
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