Cycad forensics: leaflet micromorphology as a taxonomic tool for South African cycads

Abstract

Cycads, a primitive group of gymnosperms, are currently facing extinction in many parts of the world. In South Africa, this is largely attributed to the illegal poaching of many threatened species. In the illegal trade of cycads, many highly threatened species are often deliberately misnamed as a more common species. Due to macromorphological similarity between many Encephalartos species, as well as taxonomic uncertainties that exist, species identification is also problematic. This study compared the utility of selected leaflet micromorphological characters as a taxonomic tool to independently identify eight South African cycad species. The characters, which included trichome type (if present), stomatal density and dimensions, stomatal band width and vein band width, were compared within four pairs of macromorphologically similar species. Quantitative and qualitative data on the characters were collected using stereomicroscopy, scanning electron microscopy (SEM) and variable pressure SEM. Results indicated that the majority of these characters varied significantly (p < 0.05) between paired species. Importantly, the presence of trichomes on mature leaflets of four species appears to be previously unreported. Trichome type, stomatal width and band width, and vein band width were identified as diagnostic characters that may be used to distinguish between species. The results validate the use of leaflet micromorphological characters, particularly stomatal and vein band widths (given the ease with which they can be measured), for distinguishing between macromorphologically similar cycad species.