Cytogenetical and ecological studies in some species of the Solanaceae were made in the Mediterranean-type ecosystem in Upper Egypt. The chromosome complement of Datura innoxia (2n=24) consisted of 24 median-centromeric chromosomes; that of D. stramonium (2n=24) consisted of 22 median- and two submedian-centromeric chromosomes; that of Hyoscyamus albus (2n=68) consisted of 62 median- and six submedian-centromeric chromosomes, that of H. muticus (2n=28) consisted of 21 median- and seven submedian-centromeric chromosomes; that of Withania somnifera (2n=36; new count) consisted of 27 median- and nine submedian-centromeric chromosomes; and that of Solanum nigrum (2n=72) consists of 68 median and four submedian-centromeric chromosomes. Thirty-three reproducible polymorphic bands were resulted after four RAPD-PCR primers; those bands were used for studying the genetics similarity among the species. Average similarity coefficient was ranged from 0.05 to 0.47. RAPD bands resulted after PCR: D. innoxia and D. stramonium showed five bands each; H. albus and H. muticus showed two and one bands respectively; W. somnifera seven bands and S. nigrum showed 13 bands, different patterns were produced among congeneric species. Ionic status of hot water extract of the species revealed that Hyoscyamus species was more accumulated Na⁺ and Ca⁺⁺, while Datura species accumulated more K⁺ and Mg⁺⁺ and W. somnifera and S nigrum were intermediate. These strategies of ionic accumulation were in relation to the different chromosome number of species, which might help for surviving the species in desert ecosystem.