Taxonomic significance of some leaf anatomical features of the species of Annona L. (annonaceae) from Nigeria

Abstract

A comparative study of the some leaf anatomical features of four species of Annona occurring in Nigerian was undertaken with the aid of light microscope. The four foliar structures (epidermis, petiole, midrib and lamina architecture) studied revealed useful characters which support recognition of the species. A combination of these features has been used to prepare an artificial indented dichotomous key for identifying the  species. The generic constant features encountered included hypostomata, paracytic stomatal type, linear nerves endings, uneven midrib outline, and centrally located vascular bundles in the petiole and midrib. However, the most reliable distinguishing characters found across the species included presence of brachyparacytic stomata in A. reticulata, presence of trichomes on the midrib in A. senegalensis, absence of druses on the abaxial surface in A. muricata and A. squamosa, a thick pitted anticlinal walls on the surfaces of A. muricata and consistent polygonal areola shape in A. squamosa. The overlapping characters which also justify the closeness of the species and their grouping in a genus were recorded in both the qualitative and quantitative features. Prominent among them are the mean stomatal width which is about 1.0 μm in all species, nerve endings within the areole which varies between 1-2, U- or V-shaped midrib on the adaxial surface and straight to curved anticlinal wall pattern. The significance of these observations is discussed in updating the existing data in the genus.

Keywords: Epidermis, Microscopy, Midrib, Petiole,   Systematic