Experimental taxonomy in the Epacridaceae

One hundred and thirteen species or varieties were examined for the presence of flavonoids in a chemotaxonomic study of the Epacridaceae. Species were obtained from Tasmania, Victoria, New South Wales, New Zealand and South America. Accessions from outside Tasmania contained the same general complement of flavonoids as the Tasmanian species. The characteristic flavonoids of the Epacridaceae are anthocyanins, flavonols and leucoanthocyanidins but dihydroflavones and chalcones were also present. Five common aglycones were identified i.e. cyanidin, delphinidin, kaempferol, quercetin and myricetin but pelargonidin, malvidin and possibly isorhamnetin were also present. The results suggest that myricetin may be more widespread in nature than is normally accepted, its apparent rarity being due to its lability under the conditions used in its detection. Sugars involved in glycosylation included galactose, glucose, arabinose, xylose, rhamnose and glucuronic acid. Substitution occurred characteristically at position 3 but two flavonols were glycosylated at position 5. Methylation was rare, and 3,5-diglycosylation in anthocyanins and 3,7-diglycosylation in flavonols was not observed although 3-diglycosides were common. Four pigments including cyanidin- and delphinidin-3-rhamnosylgalactoside, cyanidin-3- xylosylarabinoside and quercetin-3-xylosylrhamnoside are reported for the first time. Several species-specific compounds were observed and particularly with flavonols, chromatographic patterns proved valuable in species identification. Glycosides were found to have greater importance taxonomically than aglycones and the ratio of the major glycosidic types appears to have phylogenetic as well as taxonomic significance. The results suggest that anthocyanin and flavonol galactosides are more advanced in the family than anthocyanin arabinosides and flavonol glucnronides respectively. A correlation between chemical and cytological data enabled an evolutionary index to be calculated for 36 species, and a chemical comparison between the two subfamilies supports the opinion that the Styphelieae is more advanced than the Epacrideae. Three genera, Epacris, Cyathodes and Monotoca, have been examined in more detail than the remaining genera, and the contribution of flavonoid compounds to their taxonomy is discussed. Two new species are described for the first time. Several numerical analyses were carried out on the chemical data and a discussion of the results is given. A comparison between the Epacridaceae and published data for the related family, the Ericaceae, reveals some pronounced chemical differences, although the two are linked by the common occurrence of anthocyanin and flavonol galactosides and arabinosides. Evidence suggests that evolution towards more complex aglycones has occurred in the Ericaceae whereas greater variation in glycosylation is apparent in the Epacridaceae.