The enigmatic tribe whitfieldieae (Acanthaceae): Delimitation and phylogenetic relationships based on molecular and morphological data

Relationships of the enigmatic genera Whitfieldia, Chlamydacanthus, and Lan kesteria (Acanthaceae) were examined using molecular sequence data for two chloroplast loci (ndhF gene, trnL-trnF spacer and intron) for these and a s ample of taxa representing all major lineages within the family. Morphologi cal data, including pollen structure as imaged using SEM, were also compile d for these three genera, and evaluated in a phylogenetic context. Bremekam p suggested that Whitfieldia and Chlamydacanthus belonged together as tribe Whitfieldieae, and that Lankesteria was closely related to Pseuderanthemum in Justicieae. Contra earlier classifications of Acanthaceae, this would r esult in tribes with multiple corolla aestivation patterns. Our results con firm that Chlamydacanthus and Whitfieldia are closely related. Unexpectedly Lankesteria is sister to these two genera together and we propose that the three genera comprise an expanded tribe Whitfieldieae. Also unexpectedly, Whitfieldieae is sister to Barlerieae. We propose a number of morphological synapomorphies for Whitfieldieae including concentric rings of ridges on t he seeds and a densely granular circular area surrounding the pores of poll en grains. Chlamydacanthus and Whitfieldia further share biporate, flattene d pollen grains that are circular in outline, and seeds with glabrous surfa ces. Barlerieae is a large and diverse lineage such that synapomorphies to support aspects of their relationships are difficult to identify. However, hygroscopic trichomes on the seeds may be a synapomorphy for Whitfieldieae plus Barlerieae, with subsequent loss in Chlamydacanthus, Whitfieldia, and some Barleria. As here circumscribed, Whitfieldieae includes plants with bo th contort and imbricate corolla aestivation seconding Bremekamp's misgivin gs about basing classifications entirely upon this character.