Phylogenetic delimitation of Isoglossinae (Acanthaceae: Justicieae) and relationships among constituent genera

Phylogenetic relationships of Isoglossinae (Acanthaceae: Justicieae) were studied with a taxon sample including all but one genus putatively placed in the lineage and a dataset composed of DNA sequences from three genic regions (nrITS, cp trnS/G, trnT/L). Two members each of the lineages of Justicieae previously shown to be phylogenctically adjacent to lsoglossinae were included to test monophyly of lsoglossinae. The Malagasy genera Forcipella and Populina were excluded from lsoglossinae by our analysis. The former was placed outside of Justicieae. The latter was placed with plants representing the Tetramerium lineage of Justicieae. Our results do not provide strong support for placement of Ptyssiglottis with lsoglossinae but also cannot refute this placement. Core lsoglossinae (i.e., members of Old World Conocalyx, Isoglossa, Brachystephanus and New World Kalbreyeriella, Stenostephanus s.l., Razisea) are monophyletic; these plants share Gurtelpollen, hypothesized to be a morphological synapomorphy for the group. Malagasy Conocalyx is part of the clade that includes all sampled species of Isoglossa and does not seem distinct from the latter genus. Sister to Isoglossa (including Conocalyx) is a lineage including all sampled species of Brachystephanus plus all New World Isoglossinae. Plants belonging to this last clade share monothecous stamens as a morphological synapomorphy. Our data do not support but cannot refute reciprocal monophyly of Brachystephanus and New World lsoglossinae. There is, in fact, very little variation among these taxa such that the problem is lack of resolution rather than support for relationships that conflict with current taxonomy. NW plants in particular are richly diverse in morphology and it is remarkable that this diversification is not reflected in variation in these three DNA regions.