Relationships of the enigmatic genera Whitfieldia, Chlamydacanthus, and Lankesteria (Acanthaceae) were examined using molecular sequence data for two chloroplast loci (ndhF gene, trnL-trnF spacer and intron) for these and a sample of taxa representing all major lineages within the family. Morphological data, including pollen structure as imaged using SEM, were also compiled for these three genera, and evaluated in a phylogenetic context. Bremekamp 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 result in tribes with multiple corolla aestivation patterns. Our results confirm 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 the seeds and a densely granular circular area surrounding the pores of pollen grains. Chlamydacanthus and Whitfieldia further share biporate, flattened pollen grains that are circular in outline, and seeds with glabrous surfaces. 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 both contort and imbricate corolla aestivation seconding Bremekamp's misgivings about basing classifications entirely upon this character.

Communicating Editor: Richard Jensen