STUDIES OF ANGIOSPERM PHYLOGENY USING PROTEIN SEQUENCES

In previous papers we have reported the N-terminal 40 amino acids of the small subunit of rubisco for samples from four families of gymnosperms, nine families of monocotyledons, and 26 families of dicotyledons. We expanded this list to 122 families of dicots and derived a phylogenetic tree for all 335 species. The main computing program used was HENNIG86, with which a reliable result can be assured with only 17 taxa or less, so a major part of this paper is concerned with the strategy adopted to divide the 335 species and then to build the parts into an overall tree that is as accurate and objective as possible. Comparison with other taxonomy suggests that, at the level of placing genera into families, our methods give results that are at least 90% accurate. At higher taxonomic levels accuracy may decrease, and the result should be regarded not as a firm conclusion but as a working hypothesis for subsequent testing using the longer sequences from nucleic acids. Topics discussed include heterogeneity within species, the nature of the N-terminus of rubisco-SSU, and evidence that natural selection is powerful in determining amino acid sequence. The rate of evolution has been shown to vary between major taxa, and data suggest that angiosperms originated in the Jurassic.