Involved in the biosynthesis of germacrene-derived sesquiterpene lactones (PubMed:30468448). Component of the parthenolide biosynthetic pathway; parthenolide and conjugates are promising anti-cancer drugs highly active against colon cancer cells (PubMed:30468448). Catalyzes three consecutive oxidations of germacrene A to produce germacrene A acid (PubMed:24704560). (+)-(R)-germacrene A + 3 O2 + 3 reduced [NADPH--hemoprotein reductase] = germacra-1(10),4,11(13)-trien-12-oate + 4 H(+) + 4 H2O + 3 oxidized [NADPH--hemoprotein reductase] Secondary metabolite biosynthesis; terpenoid biosynthesis. Expressed in floral glandular trichomes. During ovary development, accumulates until the stage 3 and fades out progressively to disappear at stage 6. Belongs to the cytochrome P450 family.