Groups of closely related species belong to the same genus, which in turn are clustered into families, then orders, then classes, then phyla, and finally into kingdoms (such as the animal kingdom).

For instance, in Costa Rica, the two most closely related species are white or yellow, which prefer to mate with those of their own color.

But hundreds of thousands of older varieties and wild relatives are left to the vagaries of land-use change, global warming and chance.