O-methyltransferase involved in the biosynthetic pathway of the phytotoxin sorgoleone, a potent broad-spectrum inhibitor active against many agronomically important monocot and dicot weed species. Substrate specificity for alkylresorcinols. Strong preference for a five carbons alkyl side chain. (8Z,11Z)-5-(pentadeca-8,11,14-trien-1-yl)resorcinol + S-adenosyl-L-methionine = (8Z,11Z)-5-(pentadeca- 8,11,14-trien-1-yl)resorcinol-3-methyl ether + H(+) + S-adenosyl-L-homocysteine Homodimer. Expressed predominantly in root hairs. Belongs to the class I-like SAM-binding methyltransferase superfamily. Cation-independent O-methyltransferase family. COMT subfamily.