Contributes to cuticular wax and suberin biosynthesis. Prevents the postgenital fusion of epiderm cells in organs in contact, as well as ectopic pollen hydration and germination. Required during ovules formation. May regulate an epidermis-specific developmental program during gynoecial ontogeny. a very-long-chain acyl-CoA + H(+) + malonyl-CoA = a very-long-chain 3-oxoacyl-CoA + CO2 + CoA Lipid metabolism; fatty acid biosynthesis. Mostly expressed in epidermal cells of floral and vegetative meristems and, to a lower extent, of leaves and coleoptiles, especially in young tissues. Also present in trichomes and phloem (PubMed:10559443, PubMed:10655527). Expressed in siliques, seedlings, flowers and leaves (PubMed:18465198). Expressed in prefusion carpel abaxial and adaxial epidermis. Accumulates in ovule primordia, but restricted to chalaza in mature ovules. Also present in cells of stigmatic papillae, at the margins of ovules, and around the embryo sac. Repressed by herbicides such as flufenacet and benfuresate (PubMed:12916765). Down-regulated by darkness and low temperature, and up-regulated by salt and osmotic stress (PubMed:18465198). In additions to several malformations due to organ fusion, plants lacking FDH demonstrate an enhanced cell wall permeability, reduced trichome formation, and are female sterile. Called 'FIDDLEHEAD' because of the shape of mutants, in which adhering floral buds cause curling of inflorescence, resulting in structures reminiscent of fern fiddlehead. Belongs to the thiolase-like superfamily. Chalcone/stilbene synthases family. Truncated N-terminus.