Abstract: By this invention, methods to produce C14 fatty acids in plant seed oils are provided. In a first embodiment, this invention relates to particular C14 preferring acyl-ACP thioesterase sequences from Cuphea palustris, camphor and nutmeg, and to DNA constructs for the expression of these thioesterases in host cells for production of C14 fatty acids. Other aspects of this invention relate to methods for using other plant medium-chain thioesterases or medium-chain thioesterases from non-plant sources to provide C14 fatty acids in plant cells. In this regard, the production of C14 fatty acids in plant cells as the result of expression from an elm medium chain acyl-ACP thioesterase and a bacterial luxD gene is provided.