Farnesyl pyrophosphate synthase(FPS)belongs to the short-chain prenyltransferase family,and it performs a conserved and essential role in the terpenoid biosynthesis pathway.However,its classification,evolutionary history,and the forces driving the evolution of FPS genes in plants remain poorly understood.We analyzed 68 sequences of FPS variation patterns(2 gymnospermaes,10 monocotyledons,54 dicotyledons,and 2 outgroups)in a phylogenetic framework to identify the evolutionary forces that lead to functional divergence.The results revealed that FPS genes were under positive selection in plants.The positively selected sites were mainly located in the catalytic center and functional areas,which indicated that the 98S and 234D positive sites were important sites in the terpenoid biosynthesis pathway.They were located in the isopentenyl pyrophosphate synthase conserved domain of the catalytic site.We inferred that the diversification of FPS genes was associated with functional divergence and could be driven by positive selection.Our results showed that protein sequence evolution via positive selection is an important evolutionary force driving adaptive diversification in plant FPS proteins.We provide vital information on the classification and positive selection of FPS genes,and the results serve as useful guidance for further research on the regulation of synthetic triterpenoids and promoting their accumulation during triterpenoids biosynthesis.