Science et changements planétaires / Sécheresse


Morpho-anatomical characteristics of the leaves of Maerua crassifolia Forssk Volume 23, issue 1, Janvier-Février-Mars 2012


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Université Cheikh Anta Diop (Ucad) Faculté des sciences et techniques (FST) Laboratoire d’écologie et d’écohydrologie BP 5005 Dakar Sénégal, Université Cheikh Anta Diop (Ucad) Faculté des sciences et techniques (FST) Laboratoire de physiologie végétale Dakar Sénégal

Maerua crassifolia Forssk is a plant adapted to drought, which keeps its leaves throughout the year, even in periods of severe water deficit. Leaves of various forms and sizes of this species were sampled in the botanical garden of the Faculty of Science and Technology to study their morpho-anatomical characteristics. The samples, cut into small pieces and soaked in different solutions, were then cut into thin sections and observed under an optical microscope. Two leafy branches were also collected and were drawn. The morpho-anatomical study revealed on the one hand the presence of two types of leaves located on different branches. Hence, we could distinguish branches with alternate leaves from those with fasciculate leaves. Secondly, we discovered the presence of internal structures with adaptive traits. Indeed, the epidermis of the leaf is covered with a thick cuticle with pubescences on the upper and lower sides limiting water loss. Moreover, the leaf has stomata on both the under and upper sides which is in contrast to most xerophytic species. However, the differentiation of the mesophyll of the leaves under sunlight into palisade parenchyma and especially the presence of two rows of palisade cells on the upper side could significantly decrease evapotranspiration. Hence, the opening of the stomata of the upper face and the upper seat of the mesophyll leaf, which is exposed to light, could allow leaves to effectively absorb CO 2 through gas exchange and to reduce water loss.