PHYLOGENETIC-RELATIONSHIPS AT THE BASAL RADIATION OF ANGIOSPERMS - FURTHER STUDY BY PROBABILITY OF CHARACTER COMPATIBILITY

Difficulties in obtaining convincing angiosperm phylogenies are often attributed to widespread homoplasy among angiosperms. Direct evidence about homoplasy in individual characters can be obtained by character compatibility analysis. If two characters are incompatible, then at least one involves homoplasy. The probability of compatibility at random for two characters can be calculated or estimated by simulation. The number of compatibilities actually found for a given character can be compared with the number of compatibilities expected at random. The frequency with which a random character would receive as many or more compatibilities with other characters in the data set as the actual character is called the Frequency of Compatibility Attainment. This measure was calculated for the characters of primitive angiosperms scored by Donoghue and Doyle (1989a). Parsimony analysis of sets of characters with different frequency of compatibility attainment values show corresponding levels of homoplasy as determined by homoplasy indices. A parsimony analysis of the characters in the Donoghue and Doyle data set that have a low frequency of compatibility attainment alters some of the conclusions reached by Donoghue and Doyle regarding placement of taxa and significance of characters. The less homoplastic characters suggest that the genus Nelumbo is placed at a position near Nymphaeales rather than near Ranunculidae. Other realignments are suggested. Maximum parsimony trees based on the less homoplastic characters tend to suggest a single evolutionary origin for the chloranthoid tooth, thus suggesting that the chloranthoid tooth is homologous in all taxa that possess it. The evolutionary homology of the chloranthoid tooth is significant in that this character is preserved in the megafossil record of angiosperms and has been used to adduce relationships of ancient angiosperm lineages.