Comparative foliar epidermal micromorphology of Southern African Strychnos L. (Loganiaceae): taxonomic, ecological and cytological considerations

The micromorphology of the leaf epidermis of 11 species across four sections of southern African Strychnos was investigated using light microscopy and scanning electron microscopy. In addition to this, preliminary genome size was assessed with flow cytometry. Qualitative and quantitative results are presented for stomata, trichome and cuticular wax features with an emphasis on the abaxial epidermal surface. A correlated combination of these microscopic features was able to distinguish successfully among the 11 species of Strychnos found in the subcontinent. However, micromorphological evidence does not support the current circumscription of the sections. The often-confused S. gerrardii and S. madagascariensis are distinguishable on leaf micromorphological grounds. Stomata and trichome features show remarkable patterns that largely correlate with the ecological distribution of Strychnos species as either forest or savanna inhabitants. The significant variability in stomatal length across species is hypothesized to be indicative of possible existence of variable ploidy levels within the genus in southern African. However, preliminary genome size analyses with flow cytometry appear to be inconclusive.