“Synthetic anethole is now produced in such a pure and organoleptically acceptable quality that the anethole-carrying essential oils have little to offer in the countries where synthetic anethole is produced or readily available. In rough terms, Sweet Fennel Oil is hardly more than an anethole, modified with limonene, phellandrene and trace amounts of other components which exercise surprisingly little influence upon the odor and flavor of the oil.”
Arctander, Steffen . Perfume and Flavor Materials of Natural Origin (p. 284).