Besides that both belong to different genera, their sexual organs are also not compatible with another. As long as a platy will be crossbred with another member of the Xiphophorus genus, hybridization is possible with the exception of crossing with the comma swordtail. Comma swordtails (Xiphophorus signum) won't crossbreed with other members of the Xiphophorus genus.
Mollies can only hybridize with other members of the Poeciliidae family if their sexual organs are compatible with another. Otherwise, no hybridization will take place. Some species that can crossbreed in a natural way with mollies are guppies, endlers and limias.
