Our study is focused on the characterization of Chamaerops formations in the western of Algeria. It is based on a phytoecological approach. For this, we realized this work who aims primarily to inventory the species of Chamaeropaies in the mounts of Tlemcen, and classifying the species in biogeographic type and characterize their belonging biologic. Four representative stations of Chamaeropaies were selected. 120 floristic surveys were conducted using a minimum area of 100 m2. The survey of level different floristic performed according to the method of Braun Blanquet shows a rich vegetation of the study area with 248 species distributed in 38 families. On the biological plan 59% on average species are therophytes followed by chamaephytes with 21,75%, the hemicryptophytes is less represented with 10,25 %. Geophytes and phanerophytes remain most weakly represented with respectively 6,5% et 2,25%. On the biogeographical plan 35% of taxed, are of mediterranean origin, 8 % are West-Mediterranean, Paleo-Tempered and Circum- Mediterranean(5%), Eurasian, and European-Mediterranean are represented by 3 % for each. Globally the zone of study tends towards a therophytisation.