We report the isolation of the FIDDLEHEAD (FDH) gene of Arabidopsis by transposon tagging. Three mutant alleles of FDH carrying insertions of the Enhancer/Suppressor-mutator transposon and one stable allele with a transposon footprint were generated in the Arabidopsis ecotype Columbia genetic background. Closer examination of the adaxial epidermis of rosette leaves revealed that in addition to provoking the previously described fusion phenotype in leaves and floral organs, mutations in FDH have a deleterious effect on trichome differentiation. FDH transcripts were detected exclusively in the epidermis of young vegetative and floral organs. Plants overexpressing FDH under control of the cauliflower mosaic virus 35S promoter segregated fdh phenocopies, wild-type individuals, and plants showing severe retardation of growth and development. The dwarf plants displayed the most FDH expression, the fdh phenocopies generally the least. The protein product of FDH shows similarity to condensing enzymes involved in lipid biosynthesis, particularly those of the FATTY ACID ELONGATION family.