Phylogenetic relationships within the tribe Justicieae (Acanthaceae): Evidence from molecular sequences, morphology, and cytology

We used molecular sequence data from the nuclear ribosomal internal transcr ibed spacers and from the intron and spacer of the trnL-trnF chloroplast re gion to study phylogenetic relationships within the large (ca. 2000 species ), wide-ranging, and taxonomically difficult tribe Justicieae (Acanthaceae) . The partition homogeneity test indicated that the data sets for the two l oci were congruent, and separate analyses of the two gave similar results. Analysis of the combined data set provides a highly resolved hypothesis of relationships, much of it strongly supported. Justicieae are strongly suppo rted as monophyletic; within the tribe, five lineages and one paraphyletic grade are related as follows: [Pseuderanthemum lineage (Isoglossinae {Tetra merium lineage [multiple clades of Old World "justicioids" (Diclipterinae New World "justicioids")]})]). Many aspects of this phylogenetic hypothesi s are supported by data from morphology and cytology, and some conform to e arlier classifications of the group. There are; however, a number of novel aspects. Notably, the large genus Justicia (ca. 700 species) is not monophy letic; the Old World members form a grade and the New World members are mon ophyletic only if a number of other genera are included. The very strongly supported sister-group relationship between Diclipterinae and the New World "justicioid" lineage is novel, and ive cannot identify non-molecular synap omorphies to confirm this relationship. Rhinacanthus, a "justicioid" (Justi cia and morphologically similar general by all but phylogenetic criteria, i s strongly supported as a basal member of Diclipterinae, and cytological ev idence confirms this placement. The Pseuderanthemum lineage is only modestl y supported as monophyletic and may in fact, represent a series of basal li neages. These plants are marked by having four staminal elements (four stam ens or two stamens plus two staminodes), a plesiomorphic condition for all Acanthaceae. Additional evidence (both taxa and characters) will be necessa ry to resolve this uncertainty, as well as to determine the phylogenetic st atus of Old World "justicioids." Our analysis does provide considerable res olution of relationships within monophyletic lineages, and these relationsh ips are discussed in the context of non-molecular evidence and previous cla ssifications.