|A major clade within Acanthaceae is the cystolith clade. Cystoliths are anatomical structures found in leaves and are thought to be composed of calcium carbonate or calcium oxalate. Their function is unknown.|
Synapomorphies that distinguish Ruellieae from other lineages of Acanthaceae are little studied but may include left-contort corolla aestivation, seeds with mucilaginous hygroscopic trichomes, unequal stigma lobes, presence of a "filament curtain" (see Manktelow 2000), or combinations of the above characters. The filament curtain is a barrier formed by the fusion of four filaments that partition the corolla tube longitudinally. This structure deserves further study because of its potential taxonomic utility as well as ecological importance.
The phylogenetic hypothesis here is based on preliminary data and only a fraction of the generic diversity is represented. To date, little is known about broad-scale relationships among members of Ruellieae nor of patterns of diversity and potential causes of discrepancies among them. For example, while most of the ca. 50 genera are restricted to the Old World, much of the species diversity occurs in the New World. At present, we have no means of testing whether this pattern reflects real differences evolutionary history or alternatively, if it is merely a reflection of different working methods between New World and Old World taxonomists.
Goals of Ruellieae Project
In 2009, E. Tripp (PI) and L. McDade (Co-PI) were awarded a 3-year,$540,000 grant from the U.S. National Science Foundation. Work began in October 2009. A major goal of this project is to re-circumscribe generic diversity in Ruellieae in a biologically meaningful manner. A clearer understanding of which genera are valid and how many species they contain achieves big strides in accurately estimating standing diversity in Acanthaceae. But to re-circumbscribe genera, a thoroughly-sampled, well-supported phylogeny is necessary. At present, we are in the data generation phase needed to enable such re-circumscriptions. Ongoing work includes international fieldtrips to target and collect Ruellieae-rich geographic areas (Namibia, Ethiopia, Tanzania, southwest China, and Madagascar), sequencing of molecular markers to permit phylogenetic reconstruction, study of morphological traits through greenhouse observations, herbarium material examination, and scanning electron microscopy. This work is fostering international collaboration among botanists interested in the family and is providing training to diverse students ranging from the graduate to undergraduate level.