Phylogenetic relationships among Acanthaceae: Evidence from noncoding trnL-trnF chloroplast DNA sequences

We used sequence data from the intron and spacer of the trnL-trnF chloropla st region to study phylogenetic relationships among Acanthaceae. This regio n is more variable than,ther chloroplast loci that have been sequenced for members of Acanthaceae (rbcL. and ndhF), is more prone to length mutations, and is less homoplasious than these genes. Our results indicate that this region is likely to be useful in addressing phylogenetic questions among bu t not within genera in these and related plants. In terms of phylogenetic r elationships, Elytraria (representing Nelsonioideae) is more distantly rela ted to Acanthaceae sensu stricto (s.s.) than Thunbergia and Mendoncia. Thes e last two genera are strongly supported as sister taxa. Molecular evidence does not support monophyly of Acanthaceae s.s. although there is strong mo rphological evidence for this relationship. There is strong support for mon ophyly of four major lineages within Acanthaceae s.s.: the Acanthus, Barler ia, Ruellia, and Justicia lineages as here defined. The last three of these comprise a strongly supported monophyletic group, and there is weaker evid ence linking the Ruellia and Justicia lineages as closest relatives. Within the Acanthus lineage, our results confirm the existence of monophyletic li neages representing Aphelandreae and Acantheae. Lastly, within the Justicia lineage, we develop initial hypotheses regarding the definition of subline ages; some of these correspond to earlier ideas, whereas others do not. All of these hypotheses need to be tested against more data.