tetramerous
adjective
te·tram·er·ous te-ˈtra-mə-rəs 
: having or characterized by the presence of four parts or of parts arranged in sets of four
tetramerous flowers
Word History
Etymology
New Latin tetramerus, from Greek tetramerēs, from tetra- + meros part — more at merit entry 1
First Known Use
1826, in the meaning defined above