 <unk> is a large genus of <unk> native to Mexico , the Caribbean , Central and South America . This <unk> <unk> , non @-@ spiny genus includes both small <unk> lacking an <unk> stem and large trees . The genus has a complicated taxonomic history , and has often been split into four or five genera based on differences in the male flowers . Since the genera can only be distinguished on the basis of their male flowers , the existence of intermediate flower types and the existence of hybrids between different genera has been used as an argument for keeping them all in the same genus . This has been supported by a recent molecular phylogeny . 
