Eucalyptus cunninghamii (Myrtaceae) in the Blue Mountains of New South Wales – an Unexpected Connection between Botany and Geology

Abstract

A three-year field study of the rare Eucalyptus cunninghamii Sweet (Myrtaceae), the Cliff Mallee Ash, uncovered a hitherto unrecognised connection between this taxon and its substrate. E cunninghamii has long been known to grow on cliff edges around two valleys of the upper Blue Mountains, the Grose and the Jamison, but details of that habitat were unexplored. We show that its preferred habitat in the upper Blue Mountains is on or just downslope of a clay layer, most often the Wentworth Falls Claystone Member (WFC), and that E cunninghamii is not found elsewhere (except for an anomalous outlier near Mittagong) because the WFC is not expressed stratigraphically except around the clifflines of the two valleys. This and other environmental features delimit the distribution of E cunninghamii to a very precise geospatial range which may cause problems in times of climate change.