A. palustris Krapov., W. C. Gregory et Valls and A. praecox Krapov., W. C. Gregory et Valls, wild annual relatives of the cultivated peanut, belong to sect. Arachis. These species have qualities which deserve being incorporated into the cultivated peanut. Karyotypes were analysed, being for both species 2n=2x=18= 16m+ 2sm. The chromosome number of A. praecox is reported for the first time. Both species can be distinguished by a combination of parameters : karyotype formula, chromosome length, type and position of SAT chromosome, size of satellite and asymmetry indices. Knowledge about the chromosome number and karyotypes of both species is of great value for the improvement of cultivated peanut. The basic number x = 9 may have derived from ancestral x = 10 probably by aneuploidy. This fact supports the hypothesis that section Arachis is the one which presents the most advanced traits within the genus.