The Early History of the Proteaceae in Australia: the Pollen Record

The early history of the Proteaceae in Australia is traced from the record of fossil pollen that possess characters having taxonomic resolution among extant members of the family. Pollen characters useful for segregating subfamilies and generic groups are apertural number and form together with exine stratification and structure. When considered in conjunction with pollen shape, polarity, and size and exine sculpturing, they may be used to discriminate generic and/or species groups. The fossil pollen record suggests that the family originated in northern Gondwana during the late Cenomanian and radiated by as yet unidentified routes into southern high latitudes during the Turonian. There the family underwent substantial differentiation and expansion during Santonian–Maastrichtian times when at least four of the seven extant subfamilies evolved. Although diversification in Australia principally involved rainforest lineages (e.g. Macadamia–Helicia, Carnarvonia, Gevuina) ancestors of some sclerophyllous taxa (e.g. Adenanthos) also differentiated; this occurred in a regionalised vegetation of mesotherm open-forests in which podocarps and araucarians were important. Subsequent (Paleocene–Eocene) diversification and consolidation of the family may have focused on introduction and expansion of sclerophyllous lineages (e.g. Isopogon, Petrophile), but rainforest elements (e.g. Embothrium) were also involved. The associated vegetation, which was regionalised, experienced considerable floristic modifications during this time with introductions and/or expansion of an array of angiosperm taxa, notably Casuarinaceae, Myrtaceae and Nothofagus. In southern regions a marked decline in proteaceous pollen diversity and abundance occurred near the end of the Eocene, whereas in north-eastern regions the decline may have been later, during the Miocene.