Leaf Anatomy, Emphasizing Unusual ‘Concertina’ Mesophyll Cells, of Two East African Legumes (Caesalpinieae, Caesalpinioideae, Leguminosae)

Abstract

Cordeauxia edulis(Somalia and Ethiopia), and Stuhlmannia moavii(Tanzania, Kenya and Madagascar) are evergreen shrubs or small trees of dry areas. They have similar leaf anatomy as revealed by resin sectioning and scanning electron microscopy. The cuticle is extremely thick and all vascular bundles lack bundle sheath extensions. The most unusual feature is the mesophyll, three to seven layers consisting entirely of cylindrical palisade cells with lateral walls capable of changing vertical length by folding in a concertina-like manner. The matching outward folds of two adjacent cells always remain attached by means of a row of wall thickenings (‘pegs’). The pegs can elongate, especially so between the widely separated mesophyll cells that occupy the substomatal chamber area. The unattached flexible inward wall folds enable these ‘concertina’ cells to shorten or lengthen vertically without disrupting cell interconnections in the interior of each relatively long-lived leaf as it periodically loses and gains water. Concertina cells may be an anatomical adaptation allowing these leaves to remain evergreen and survive extended periods of drought and yet to store water quickly when it becomes available.