O-methyltransferase involved in the biosynthesis of coumarins natural products such as daphnetin derivatives (PubMed:12480941). Catalyzes specifically the methylation of daphnetin (7,8-dihydroxycoumarin) to produce hydrangetin (7-hydroxy-8-methoxycoumarin) (PubMed:12480941). Probably involved in acclimation to low temperature conditions (PubMed:12480941). 7,8-dihydroxycoumarin + S-adenosyl-L-methionine = 7-hydroxy-8-methoxycoumarin + H(+) + S-adenosyl-L-homocysteine Aromatic compound metabolism. Secondary metabolite biosynthesis. Induced by cold and photosystem II excitation pressure by high light illumination. Belongs to the class I-like SAM-binding methyltransferase superfamily. Cation-independent O-methyltransferase family. COMT subfamily.