Studies on the leaf epidermal characters and petiole anatomy of four species of Citrus L. viz., C. limon (L.) Burm., C. paradisi Macf., C. reticulata Blanco and C. sinensis (L.) Osbeck were carried out to establish and document their foliar anatomical characters with the aim of separating them from the modified varieties been cultivated globally. Leaf epidermal features that revealed close relationship among these taxa include hypostomatic condition, stomata shape and type, presence of secretory cavity on the adaxial surface, and polygonal shape of epidermal cells. The absence of secretory cavity on the abaxial surface separates C. limon and C. sinensis from others. Petiole anatomy revealed that the outline is flat without ribs in C. sinensis, convex with short ribs in C. reticulata, convex with long ribs in C. paradisi while in C. limon it is circular without ribs. Presence of trichomes and crystals distinguishes C. paradisi from the rest.

Morphological studies of the leaves of ten species in the family Euphorbiaceae collected from three different locations with different pollution levels in Southwestern Nigeria were carried out in order to establish the effect of air pollution on these species. The study was carried out in both dry and wet seasons. Climatic data and pollutants concentration levels of the study sites were determined. Leaf area of all the species was measured using an established nondestructive method while petiole length was determined using metric ruler. The result showed that most species showed significant reductions (p<0.05) in the leaf area and petiole length across the three locations and this reduction is from rural to suburban to urban areas. Among all the species that showed reductions in leaf area, Alchornea cordifolia showed the highest response while Euphorbia hyssopifolia, E. hirta and Crotonlobatusdo not show clear reductions. Similar significant reductions were recorded for petiole length with the highest impact recorded in Manihot esculenta while species like E. hyssopifolia, E. hirta, C. lobatus and Flueggea virosa were not significantly reduced. This study showed that plants generally respond to air pollution with reduction in foliar morphology and the response is species specific.