This issue of the OBPE Scientific Bulletin (No. 5) is dedicated to the late Ordinary Professor Balthazar MPAWENAYO to whom we pay tribute in his capacity as a professor and researcher of high level. He was born in Gisozi on 23 June 1953 and died on 11 August 2020 after a short illness. He participated in raising the level of students and his colleagues through quality teaching, including good end-of-year dissertations. His colleagues and students were also able to appreciate the quality of his scientific publications. He has contributed enormously to the work of INECN, currently OBPE, in various fields of the Environment and the conservation of biodiversity. In this special issue, his former colleagues and friends at work, his former students who followed in his footsteps by currently becoming, like him, great professors, executives of the University of Burundi and the Ecole Normale Supérieure and researchers in various institutions, pay tribute to him by publishing in this issue themes related to the former concerns of the late Professor MPAWENAYO. These were focused on Botany including plant systematics, Algology, Biodiversity and its Conservation, Ecology and Ethnobotanical studies. Dear colleague and friend, the team of researchers you formed remains aware that you left so early, with no doubt many other plans for the future. Know that you are missed by everyone who knew you. We have memories of you of a Professor who had a sense of humor and loved to smile but who always sought perfection in scientific research. Through this issue, know that all those whose level you have helped to raise will follow your example to improve the quality of research and thus contribute to the development of our dear country, Burundi.