The increasing narrowness of the rural space, the very frequent overgrazing and the effect of human activities lead to a very quick natural vegetation damage and to genetic erosion. This type of regressive evolution has been pointed out in Tunisia. A prospecting program was initiated in 1984 in order to collect species belonging to Medicago genus. Their distribution areas linked to rainfall and soil parameters are reported and their agronomic description proposed and, some aspects of floral biology and fecundation traits are developed. The study of six polymorphic loci enable us to specify the natural reproduction biology of Medicago ciliaris and Medicago intertexta. As far as Medicago orbicularis is concerned, electrophoretic variability analysis of eight isoenzymes show them strictly homozygous in twelve populations, and confirm the highly autogamous regime of this species; while the same isoenzymatic analysis reveals an important polymorphism for Medicago polymorpha and at a lower level for Medicago truncatula. At end, facultative autogamy, as well as aptitude to propagate by vegetative way appears as adaptive ways for the perennial Medicago sativa ssp. tunetana for which the isoenzymatic polymorphism analysis reveal a continuous variability range within the prospected areas.