Morpho-stomatal variation of Acacia species in some parts of the Sudano-Sahelian savanna zone of Nigeria

Acacia is a member of the Fabaceae family, but classifying its species has proven challenging due to their extensive distribution. A study was conducted to assess the morphological differences in the leaves, thorns and inflorescence of various Acacia species located in the Sudano-Sahel region for accurate taxonomic identification. Eleven Acacia species were classified based on qualitative and quantitative morpho-stomatal traits. Generally, most species had alternate, bipinnate compound leaves with oblong pinnules. However, A. senegal showed obovate pinnules, A. auriculiformis had simple curved (sickle-like) leaves and A. gourmanensis featured bilobed simple leaves. Leaf textures varied from smooth (glabrous) to hairy (pubescent) and all species exhibited entire leaf margins. Inflorescence and leaf lengths were generally less than 0.9 cm, except for A. auriculiformis and A. gourmanensis, which had 13.25 cm and 1.29 cm, respectively. Leaf width and leaf area were highest in A. auriculiformis, with 1.00 cm and 2.73 cm², respectively, whereas the remaining investigated species had values lower than 1.00 cm. All flower pedicel length results were less than 0.10 cm. A. auriculiformis and A. gourmaensis had 0.07cm, while A. nilotica and A. senegal had the lowest recorded values at 0.01 cm. There was no significant variation in the trichomes and stomatal type of foliar micro-morphological features; they only differ in terms of size, which can be attributed to their adaptation. Future study on the vascular bundle and the chemical composition of the documented species is paramount.