Le projet "Dahomey Gap": une contribution à l'histoire de la végétation au Sud-Bénin et Sud-ouest du Nigéria

La coupure que l'on constate dans les forêts denses africaines au niveau du Togo et du Bénin soulève de nombreuses questions sur les rapports forêt/savane au cours des derniers millénaires. Le projet Dahomey Gap vise à y répondre, par une approche pluridisciplinaire intégrant botanique et histoire de la végétation dans le Sud-Bénin et le Sud-Ouest du Nigéria. A partir de travaux déjà avancés sur la végétation du Bénin et des premières prospections palynologiques, quelques aspects du projet sont exposés ici: tels la caractérisation des différentes formations forestières du Bénin, les premiers résultats sur l'histoire holocène de la végétation du Sud-Bénin (mangroves, forêts, savanes) enregistrée depuis près de 7000 ans dans les lagunes

Chemical constituents and antimicrobial properties of Phyllanthus amarus (Schum & Thonn)

The chemical composition of the leave extracts of Phyllanthus amarus (Schum and Thonn) of the family Euphorbiaceae from Nigeria was analyzed by GC-MS. The extracts were also examined for their potential to inhibit the growth of clinical isolates following standard procedure. The major compounds identified in the hexane extract are a flavonoid, flavone 4’,5,7-triethoxy-3,3’,6- trimethoxy (20.23%) and a triterpenoid 17-(1,5-Dimethylhexyl)-6-hydroxy-5-methylestr-9-en-3-yl acetate (19.02%) while bufalin (18.71%) and tetratetracontane (12.91%) were the major compounds detected in the methanol extract. Steroidal triterpenoids are the major compounds present in the extracts as it accounted for 47% of the total detectable content in the hexane extract and 52% in the methanol extract. The steroidal triterpenoids which exist primarily as acetate in the hexane extract include cycloeucalenyl acetate, ergosta-5,7,22-trien-3-ol acetate, macdougallin, 17-(1,5-Dimethylhexyl)-6-hydroxy-5-methylestr-9-en-3-yl acetate, stigmasterol and β-sitosterol while the methanol extract contains 6,7-epoxypregn-4-ene-9,11,18-triol-3,20-dione, 11,18-diacetate, bufalin, olean-13(18)-ene, methyl ursolate, barringenol R1 and 7,8- epoxylanostan-11-ol,3-acetoxy. Hexane extract of the plant exhibited antifungal activity on Candida albicans while methanol extract revealed significant antibacterial activity on Pseudomonas aeruginosa and Staphylococcus aureus at all concentrations of the extract between 12.5 and 100 mg/mL, the activity being comparable to the standard antibacterial drug, Oxacillin. The leaves of Phyllanthus amarus is a potential source of steroidal triterpenoids which could serve as biomarker for the plant species. The extracts of the plant may also serve as a natural source of antimicrobial agents for the treatment of some microbial infections.Keywords: Phyllathus amarus, antimicrobial, phytochemicals, leaf extract

African pollen database inventory of tree and shrub pollen types

African pollen data have been used in many empirical or quantitative palaeoenvironmental reconstructions. However, the pollen types used in these studies were not controlled and standardised, preventing the precise understanding of pollen-plant and pollen-climate relation that is necessary for the accurate quantification of continental scale climate change or ecological processes in the past. This paper presents a summary of the progress made with the African Pollen Database (APD) inventory of plant diversity from pollen data extracted from 276 fossil sites and more than 1500 modem samples, with a focus on tropical tree pollen types. This inventory (1145 taxa) gives, for each pollen taxon whose nomenclature is discussed, information on the habit, habitat and phytogeographical distribution of the plants they come from. Special attention has been paid to pollen types with similar morphology, which include several plant species or genera, whose biological or environmental parameters can differ considerably