Providing some pharmacopoeial standards for the leaves of two closely-related <i>Alstonia</i> species

Abstract

Background: Alstonia boonei De Wild. and Alstonia congensis Engl. (Apocynaceae) are commonly used by the indigenes of Nigeria to treat malaria and other ailments.

Objective: This study has examined the leaves of A. boonei and A. congensis with a view to providing some pharmacopoeial standards for identification and development of their individual monograph.

Materials and Methods: Macroscopic and microscopic studies were carried out on the leaves of A. boonei and A. congensis with the use of light microscope, while the proximate and fluorescence analyses were carried out according to standard World Health Organization specifications.

Results: The leaves of A. boonei and A. congensis were coriaceous. The quantitative microscopy of the leaves showed the upper epidermal cell lengths for A. boonei and A. congensis as 32.5 ± 0.56 (μm) and 38.5 ± 1.8 (μm), while palisade ratios were 5.2 ± 0.4 and 3.7 ± 0.2, respectively. The stomata numbers of A. boonei and A. congensis were 5.0 ± 1.2 and 1.8 ± 0.3, respectively. The stomata length and width of A. boonei, respectively, were 24.5 ± 0.5 (μm) and 22.0 ± 1.2 (μm), while those of A. congensis, respectively, were 35.0 ± 0.8 (μm) and 28.0 ± 3.0 (μm). The vascular bundle in A. boonei was arc-shaped with xylem vessels standing in isolation but assuming a U-shape in A. congensis with xylem vessels interlocking to form a crown-like connection. Vein-islet number of A. boonei (9.0± 0.7) was slightly more than that of A. congensis (8.8±1.8). Total ash values and moisture contents of the leaves of A. boonei and A. congensis were 8.5 ± 0.01 and 6.8 ± 0.03; and 9.1 ± 0.04 and 9.9 ± 0.02, respectively.

Conclusion: The foliar epidermal and anatomical characters presented in this study are useful for differentiating between the two closely-related species, Alstonia boonei and Alstonia congensis. The established characters in each of the species could be incorporated into the next editions of the Nigerian and West African Herbal Pharmacopoeias.

Keywords: Alstonia spp., Pharmacopoeia, Microscopy, Proximate analysis, Organoleptic evaluation