Vegetable sheep : a chemosystematic study of the Cassiniinae

• Main Author: Reid, Alan
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/4769

It is well known that there are few places in the Asteraceae where generic limits are more difficult to apply in practice than in the tribe Gnaphalieae subtribe Cassiniinae. This is the subtribe of the paper daisies, the Edelweiss, the cudweeds. These species are characterised by discoid floral heads with papery involucral bracts. This thesis presents the results of an investigation of the flavonoid chemistry of the major species present in Australasia from which an attempt to infer taxonomic relationships among the species based on the combination of chemical, morphological and ecological characters is made. The exudate and vacuolar flavonoid profiles of six genera Cassinia R. Br., Ozothamnus R. Br., Raoulia Hook, f and Haeckeria F. Muell., Leucoqenes R. Br. and Lawrencella Anderberg were established. The exudate chemistry consists of chalcones, dihydrochalcones and flavanones, several of which lack B-ring oxygenation, and quercetin 3-0- and 7-0-methyl ethers. Vacuolar flavonoids include galangin, eriodictyol-7-O-methyl ether, and a series of kaempferol and quercetin glycosides. Several combinations of these compounds occur in the taxa studied. Species in this study form a number of relationships that show a strong correlation to geography, altitude and ecological conditions. The production of exudate flavonoids show a direct correlation to the amount of UV-B radiation. These relationships mimic the classical taxonomy proposed by Allan in 1961 for the New Zealand species and by Burbidge in 1958 for the Australian species. Differences in distribution of flavonoids are taken as evidence for recognition that the relationships between the genera are as complex as classical taxononomic studies suggest.