β-Phellandrene synthase (neryl-diphosphate-cyclizing) (EC 4.2.3.51, phellandrene synthase 1, PHS1, monoterpene synthase PHS1) is an enzyme with systematic nameneryl-diphosphate diphosphate-lyase (cyclizing; beta-phellandrene-forming).[1] This enzyme catalyses the following chemical reaction