Application of evidence from molecular biology to the biogeography of angiosperms

Abstract

Previously published sequence data from species, whose ancestors are thought to have been separated during the break-up of Gondwanaland, yield mean number of inferred nucleotide differences (i.n.d.) for two comparisons, Africa versus Australia and New Zealand versus Australia. In the geophysical literature, the dating of these separations appears to be uncontroversial, viz. 130 Ma and 80 Ma respectively. The mean rates for the two comparisons are one i.n.d. in 11.7 Ma and 11.9 Ma. The similarity of these estimates encouraged us to deduce the dates of other events for which we present new data. The deepest division detected within the angiosperms corresponds to 244 Ma (Triassic). This is compared with recent equivalent datings. The division between representatives of northern primitive families (Magnoliaceae, Calycanthaceae) and southern primitive families (Winteraceae, Idiospermataceae) corresponds to 162 Ma (Upper Jurassic). This is discussed briefly in relation to geophysical information. Although there is considerable scope for error in this approach, it is considered to be worth pursuing in the light of the imminence of more and longer sequences from nucleic acids and of the interest and difficulty of such biogeographical problems.