This work concerns the flora and vegetation of Algerian arid lands extending over nearly 25 million hectares. From a phytogeographic point of view, from North to South and West to East, this region ensures the transition between, on the one hand, the Mediterranean and Saharo-Sindian flora, on the other hand, the Western and Eastern flora. This contribution aims to study life strategies sensu Grime (1977), as well as the biological and phytogeographic species diversity. It is part of a series of studies that we have carried out on biodiversity and the climate in Algeria and particularly in arid zones since 1998. Our approach is based on a set of floristic and mesological field samples. Six large plant vegetation units called "formations" are highlighted by factorial correspondence analysis. The partial analyzes of these six groups individualize eighteen groupings. Among these groupings, we note the importance of psammophilic and degradation groups, which represent 44% of the total. The analysis of Grime C.S.R. shows a general dominance of stress-tolerant-ruderal "SR" (35-47%) and stress-tolerant "S" s.l. (64-74%). The ruderal "R" and stress-tolerant (SR) species form a pool of species common to all formations with relatively high abundance. The analysis of biological diversity emphasizes the role of annual species (47%) within these plant formations. It is necessary to underline the life strategies complementarity of the three simplified biological types and the adaptive specificity of each of them.At the phytogeographic level, we note the importance of Mediterranean taxa (50%), followed by endemics (15%), Saharo-Arabians (14%) and link (liaison) taxa (9%).From this phytogeographic analysis emerge an eastern and western endemism with an overall plant endemism rate equal to 15%, the phytogeographical originality of this area is emphasized. The Algerian steppe faces multiple constraints due essentially to anthropic action that can be aggravated by drought periods. Promoting a conservation strategy with the creation of protected areas combined with the anthropic pressure reduction appears to be one of the main options to be considered on this territory of high heritage value.

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