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.

Origins of the southeastern Australian vegetation

“…Presumably similar forcing factors impacted on other, less well known, fossil taxa in the region. Conifers were extremely common in Oligocene southeastern Australia (Hill & Brodribb 1999) and some demonstrate trends in leaf size and stomatal distribution in response to climate change (Hill & Carpenter 1991). In Tasmania during the Early Eocene, Dacrycarpus had relatively large leaves in flattened shoots, but by the Early Oligocene small-leaved imbricate shoots predominated, suggesting Dacrycarpus moved from the understorey to the well lit forest canopy (Brodribb & Hill 1998), similar to its extant niche.…”

Reproductive traits of tropical rain-forest trees in New Caledonia

“…The present biota is probably best viewed as a mixture of ancient and recently immigrant taxa, with an evident post-Eocene radiation of certain groups such as Araucariaceae (Setoguchi et al 1998). The presence of clearly relictual taxa such as Acmopyle (Hill & Carpenter 1991) is indicative of a continuously favourable moist climate, perhaps throughout the Cenozoic. Ecological processes in New Caledonian rain forests are not well understood, and there are few published reports.…”

When did the mistletoe family Loranthaceae become extinct in Tasmania? Review and conjecture

“…data) grew in floristically diverse, warm temperate rainforest dominated by Nothofagus and gymnosperms that are now extinct in Tasmania. For example, trees included a species similar to Nothofagus moorei, now endemic to NSW, Podocarpaceae, including Acmopyle, now endemic to New Caledonia and Fiji, and an extinct Araucaria belonging to the South American section Columba: Average leaf lengths in the Loch Aber fossil flora are smaller than in early Eocene floras, consistent with a general decrease in mean air temperatures from the early to middle Eocene (Hill and Carpenter 1991;Carpenter et al 1994).…”