STUDY OF THE LICHENS OF THE MEHDIA' KASBAH, HISTORICAL MONUMENT OF KENITRA, MOROCCO

Abstract The aim of this study is to inventory and describe the lichenic flora that colonizes the Kasbah walls of Mehdia (Ksar Moulay Ismail), a historical monument in Kenitra. The Kasbah of Mehdia had an aesthetic and architectural value and has suffered over time various alterations. Building materials around the world are exposed to various degradation factors and alteration caused by the climate, living things (biological) and time. The alterations of the monuments can be grouped into three main categories: physical, chemical and biological. The lichen species encountered are Dirina ceratoniae Mont., (1849), Dirinamassiliensis f. massiliensis Durieu & Mont., (1848), Roccellaphycopsis (Ach.) Ach., (1810) and Verrucaria minor Breuss, (2007). These species can cause with other environmental factors the deterioration of building materials of the Kasbah. Lichens can be the cause of modifications of the surfaces of the stones of the monuments by the bio geophysical and bio geochemical processes. Bio-geophysical changes are caused by hyphal penetration beneath the stone surface and contraction and expansion of the lichen and chemical alterations produced by lichens are due to the substances they secrete: oxalic acid, the carbon dioxide produced by respiration.