Comparative leaf and stem anatomy in selected species of Ruellieae (Acanthaceae) representative of all major lineages

Abstract

With more than 1,200 species, Ruellieae is a taxonomically and ecologically diverse tribe in the Acanthaceae. In recent years, numerous morphological and phylogenetic studies have contributed important new information about species belonging to this tribe, yet basic anatomical knowledge of lineages within Ruellieae is relatively scarce. The objective of the present study is to help close this anatomical knowledge gap through comparative leaf and stem anatomical study of 14 species representative of all seven subtribes within Ruellieae. We document relative conservatism in leaf and stem anatomy except that unifacial leaves characterise a few taxa and have evolved a minimum number of three times in the tribe. Cystoliths were found abundantly in both leaf and stem tissue; these were oriented in two different directions in leaves while in stems only one orientation was found. Finally, we discuss the putative presence of a stem and petiole endodermis in several taxa studied. These data serve as a starting point for further comparative anatomical studies within Ruellieae and other Acanthaceae.