Methyltransferase involved in phenylpropanoid polyamine conjugate biosynthesis. In vivo, methylates only one of the 5-hydroxyferuloyl moieties of N1,N5,N10-tri-(hydroxyferuloyl)-spermidine, while is able in vitro to convert all three 5-hydroxyferuloyl residues to the corresponding sinapoyl moieties and to methylate caffeoyl CoA and tricaffeoyl spermidine. Binds 1 divalent metal cation per subunit. kcat is 0.0029 sec(-1) with caffeic acid as substrate. kcat is 0.0025 sec(-1) with quercetin as substrate. kcat is 0.0141 sec(-1) with caffeoyl CoA as substrate. kcat is 0.0239 sec(-1) with caffeoyl glucose as substrate. kcat is 0.0301 sec(-1) with chlorogenic acid as substrate. Aromatic compound metabolism; phenylpropanoid biosynthesis. Expressed in inflorescences and flower buds. Not detected in roots, leaves or stems. Located exclusively in the tapetum of developing stamen. Expressed only in early stages of flower development. Belongs to the class I-like SAM-binding methyltransferase superfamily. Cation-dependent O-methyltransferase family. CCoAMT subfamily.