A study of the genus Senna (Caesalpinioideae, Cassiinnae) in South Africa

Gomphocarpus physocarpus E.Mey. is a short shrub of the Apocynaceae family that is native to southern Africa.Gomphocarpus physocarpus is traditionally used to produce ointments for the treatment of warts and the seeds are used in rituals.The leaves and stems produce milky latex that is toxic, yet it has never been described in detail particularly with regards to the anatomy of lactiferous cells.The present study was undertaken to examine the distribution, structure and chemical composition of the laticifers in the leaves and stems of G. physocarpus.Histochemical methods and light microscopy were used.In addition to studying the internal laticiferous structures, the indumenta of the leaves were examined.Leaf surface imaging with stereomicroscopy and SEM revealed the presence of non-glandular trichomes which appeared ribbon-like, segmented and torulose with cuticular warts.The trichomes appeared to be concentrated on the emergent leaves, possibly conferring protection to the immature plant structures against insects and herbivores.The laticifers in the leaves were associated with the vascular system of the midrib and the larger lateral veins.Stem longitudinal and cross sections stained with safranin and fast green revealed the presence of laticifers in the pith, cortex and external to the phloem.Laticifers in the stems were branched, nonarticulated and parallel to the longitudinal axis.The main compounds accumulated in the laticifers were phenols and alkaloids.Phytochemical screening of leaf and stem crude methanolic extracts displayed positive reactions for carbohydrates, cardiac glycosides, terpenoids, alkaloids and phenols.This study provides a foundation for future phytochemical and pharmacognosy work on this species.Additionally, the presence of laticifer systems in G. physocarpus could be of taxonomic importance, considering that this is the first report of its presence in this genus.