Evolution of Acmopyle and Dacrycarpus (Podocarpaceae) foliage as inferred from macrofossils in south-eastern Australia

Abstract

Macrofossil specimens of Dacrycarpus and Acmopyle from south-eastern Australia are investigated. The specimens previously assigned to D. praecupressinus are revised, with one placed in a different genus and new species, Podocarpus witherdenensis, and some placed in a new species, D. latrobensis. One specimen is retained as the lectotype of D. praecupressinus. Dacrycarpus eocenica is re-examined and it is concluded that this species is not Dacrycarpus, but probably belongs to an extinct podocarpaceous genus. Dacrycarpus setiger is transferred to Acmopyle, and three new Acmopyle species, A. florinii, A. glabra and A. tasmanica, are described. It is hypothesised that during the Tertiary in south-eastern Australia stomatal distribution was reduced on Dacrycarpus and Acmopyle foliage. In Dacrycarpus the bilaterally flattened foliage type (which has a greater photosynthetic area than the bifacially flattened foliage) became rare or extinct after the Early Oligocene, prior to the extinction of the genus in the region. Acmopyle has not been recorded in the region after the Early Oligocene. A trend towards reduction in leaf size at high latitudes has previously been demonstrated in angiosperms but not gymnosperms and, along with the reduction of stomatal distribution, probably represents convergent evolution in response to climatic change.