Accessions of eight Lycopersicon species and five yellow-flowered Solanum species were used as males in crosses with 2x and 4x L. esculentum to observe seed set and progeny ploidy. Species which failed in crosses to L. esculentum were crossed as males to 2x and 4x L. peruvianum. In cases of low seed set, chromosome counts were undertaken to establish the nature of the progeny. Endosperm Balance Number (EBN) relationships were determined for the crossability groups. Results support the basic concept of an L. esculentum crossability complex and an L. peruvianum crossability complex. Within the L. esculentum complex, all EBNs appear identical with a value of 2. Within the L. peruvianum complex, more variability appears to exist. The EBN values of this group are higher, and may be approximately double those of the L. esculentum complex. The EBN of L. peruvianum var 'humifusum' appears to be somewhat lower than other L. peruvianum types. The EBN values of S. lycopersicoides, S. rickii, S. ochranthum and S. juglandtfolium could not be determined experimentally. Differential aspects of Lycopersicon and tuber-bearing Solanum evolution may be interpreted on the basis of endosperm compatibility.