AbstractIn order to study the mode of action of herbicides we conducted a pilot study analysing phenotype and gene expression of flufenacet‐ and benfuresate‐treated Arabidopsis thaliana (L) Heynhoe plants. Treatments with either herbicide caused phenocopies of the known Arabidopsis mutant fiddlehead, displaying fused organs and the typical fiddlehead‐like inflorescence. Herbicide treatments of other plant species, including monocots, also gave rise to analogous organ fusions, indicating the presence of the target in a broad range of plants. Furthermore, many other herbicides with a proposed similar mode of action, eg chloroacetanilides, produced comparable fusion phenotypes in plants. The fiddlehead gene encodes a putative very‐long‐chain fatty acid elongase (VLCFAE), which corroborates earlier biochemical results pointing to the inhibition of VLCFA synthesis as mode of action of flufenacet. Gene expression profiles of herbicide‐treated plants using the first 8247 gene Arabidopsis gene array of Affymetrix provided additional clues in support of inhibition of VLCFA synthesis. We discuss fiddlehead‐like elongases as plant specific targets for flufenacet and many other herbicides. Copyright © 2003 Society of Chemical Industry