Chromosome morphology at pachytene was studied in two species; A. sp. (GKP 9990, Section. Erectoides) and A. villosulicarpa (Section. Extranervosae) and compared with the other sectional species. The genus Arachis appeared to be based on a basic karyotype of six differentiated chromosomes, three specialised chromosomes and one nucleolus organizer. The karyotypes of species belonging to sections Erectoides, Triseminale and Extranervosae appeared to be more primitive than sections Arachis and Rhizomatosae. The section Arachis appeared to be a natural group of cross-compatible species having the characteristic A chromosome with the exception of A. batizocoi. The pachytene chromosome morphology did not indicate a highly marked chromosomal differentiation between the A' and ‘B’ genomes assumed to be present in the cultivated groundnut. Specific differences have been thought to be brought about in the genus Arachis through minor structural repatterning and major genetic differentiation.