Development and Functions of Leaf Bases in Leaf-Succulent Curio P.V. Heath (Asteraceae)

The leaf base in dicots, unlike that in monocots, rarely grows into a leaf sheath and it usually remains barely discernible in the definitive leaf. As a result, the leaf base is frequently overlooked when studying the morphogenesis of dicot leaves. The lack of information of the development of leaf bases in dicots with different morphological leaf types hampers comparing the morphogenesis of their leaves with the morphogenesis of monocot leaves of similar morphological types. The theory of two zones which is generally used in studies of monocot leaf morphogenesis is shown to be quite applicable to the morphogenesis of unifacial, subunifacial, and bifacial leaves of members of the genus Curio (Asteraceae). However, in the investigated species of Curio, these two zones become clearly discernible only after the leaf has begun to grow intercalary. The leaf bases in these species are shown to be quite similar with monocot leaf bases in their protective function as they sheath the younger growing leaves in the bud. The lateral growth of the leaf base to result in spanning a large part of the stem circumference is concluded to be a xeromorphic trait of Curio species. The leaf bases in two species develop adaxial depressions to embrace the younger growing leaves to better protect them.