The Study of Plant Phylogeny Using Amino Acid Sequences of Ribulose-1,5-Bisphosphate Carboxylase. IV. Proteaceae and Fagaceae and the Rate of Evolution of the Small Subunit

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Abstract
N-terminal, 40 amino acid sequences of ribulose bisphosphate carboxylase small subunit (SSU) are given for four species of Proteaceae, six of Fagaceae including four from Nothofagus, and seven from Solanaceae including six new sequences from Nicotiana. Phylogenetic trees, regarded as tentative since only one protein is involved, are given for each of the three groups and approximate positions of the families in the angiosperm tree are indicated. An example of the destabilizing of a hitherto invariant site is given. Working from the 'molecular evolutionary clock' hypothesis, and deriving time from plate tectonics, the data from both Proteaceae and Nothofagus lead to rates of evolution of SSU of one non-silent nucleotide substitution per 9 My. This agrees with an early Cretaceous origin of the angiosperms. A test is proposed to distinguish distributions that are the result of 'vicariance biogeography' from those due to 'dispersal biogeography'. It is concluded that distribution of Nicotiana is most likely due to dispersal.