Eucalyptus fruits in stratigraphic context in Australia

Abstract

THE eucalypts are the outstanding group of Leptospermeae (subfamily Leptospermoideae of Myrtaceae) and of the whole Australian flora¹. There are over 500 species of eucalypts, nearly all restricted to Australia. The origin of this remarkably diverse and successful genus has been a matter for speculation. The comparitively well known Tertiary palynological record is of little assistance in answering these questions, as spores and pollen have insufficient properties to identify the genus. Hence only the macrofloral record is taxonomically significant. Although Tertiary macrofossils⁴ are abundant, the fossil record of Eucalyptus and even Leptospermoideae is poorly known^2,3. The first unequivocal fossil gumnuts (Eucalyptus fruits), of indefinite age, were identified only recently from silicified floras near Woomera⁵, in South Australia's present arid zone. These specimens were collected without reference to the stratigraphy. However, we have now collected specimens from similar silicified outcrops near Stuart Creek (Fig. 1), where their probable age may be deduced by correlation of the sediments with Tertiary sequences elsewhere in South Australia. Eucalyptus can now be placed in stratigraphic context.