There are problems in the delimitation/identification of Plectranthus species and this investigation aims to contribute toward solving such problems through structural and histochemical study of the trichomes. Considering the importance of P. zuluensis as restricted to semi-coastal forests of Natal that possess only two fertile stamens not four as the other species of this genus. The objective of this work was to study in detail the distribution, morphology and histochemistry of the foliar trichomes of this species using light and electron microscopy. Distribution and morphology of two types of non-glandular, capitate and peltate glandular trichomes are described on both leaf sides. This study provides a description of the different secretion modes of glandular trichomes. Results of histochemical tests showed a positive reaction to terpenoids, lipids, polysaccharides and phenolics in the glandular trichomes. We demonstrated that the presence, types and structure of glandular and non-glandular trichomes are important systematic criteria for the species delimitation in the genus.

Antioxidant and acetylcholinesterase inhibitory activity of the three species namely, Endostemon obtusifolius (E. Mey. ex benth.) N. E. Br, Plectranthus zuluensis (T. Cooke) and Tetradenia riparia (Hochst.) Codd. were evaluated. Maximum antioxidant activity was exhibited by E. obtusifolius (IC50 130 ?g/ml) followed by T. riparia (IC50 142 ?g/ml) and P. zuluensis (IC50 169 ?g/ml). Acetylcholinesterase inhibition (AChEI) was highest in P. zuluensis (IC50 290 ?g/ml) followed by E. obtusifolius (IC50 470 ?g/ml) and T. riparia (IC50 750?g/ml). The results suggest that these three species possess natural antioxidants and acetylcholinesterase inhibitors, which may be beneficial for the treatment of Alzheimer’s disease, that require high concentration of these compounds. DOI: http://dx.doi.org/10.3329/bjb.v43i3.21606 Bangladesh J. Bot. 43(3): 331-335, 2014 (December)

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