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 le ast 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 fr equency with which a random character would receive as many or more co mpatibilities with other characters in the data set as the actual char acter is called the Frequency of Compatibility Attainment. This measur e 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 corre sponding levels of homoplasy as determined by homoplasy indices. A par simony analysis of the characters in the Donoghue and Doyle data set t hat have a low frequency of compatibility attainment alters some of th e conclusions reached by Donoghue and Doyle regarding placement of tax a and significance of characters. The less homoplastic characters sugg est that the genus Nelumbo is placed at a position near Nymphaeales ra ther than near Ranunculidae. Other realignments are suggested. Maximum parsimony trees based on the less homoplastic characters tend to sugg est a single evolutionary origin for the chloranthoid tooth, thus sugg esting that the chloranthoid tooth is homologous in all taxa that poss ess it. The evolutionary homology of the chloranthoid tooth is signifi cant in that this character is preserved in the megafossil record of a ngiosperms and has been used to adduce relationships of ancient angios perm lineages.