THE UTILITY OF ATPB GENE-SEQUENCES IN RESOLVING PHYLOGENETIC-RELATIONSHIPS - COMPARISON WITH RBCL AND 18S RIBOSOMAL DNA-SEQUENCES IN THE LARDIZABALACEAE

The chloroplast gene atpB was sequenced for seven genera of the Lardiz abalaceae and three outgroup taxa to assess its utility as a source of phylogenetic information. The resulting phylogenetic tree was compare d with trees based on 18S nuclear ribosomal DNA and rbcL (chloroplast DNA) sequences, as well as a combination of all data (atpB, 18S, and r bcL) for the same taxa. Sequence divergence values, statistics related to patterns of character transformation, and indices measuring homopl asy and branch support were also compared. The topology of the trees d erived from atpB, 18S, and a combination of all three sequence data se ts were largely congruent. All phylogenies, with the exception of the tree derived from rbcL data, supported the monophyly of the Lardizabal aceae. All indicators of nucleotide substitution rate suggest that rbc L is the least conserved, atpB is intermediate, and 18S is the most co nserved of the three genes sequenced. Measures of homoplasy also indic ate that the rbcL tree is less strongly supported than those based on atpB, 18S, or a combination of atpB, 18S, and rbcL sequence data.