Although isocyanides are not rare amongst terrestrial microbes and marine organisms, despite tens of thousands of natural products isolated from plants, isocyanides are still missing. Isocyalexin A is the first isocyanide of plant origin. Isocyalexin A was isolated from UV-irradiated rutabaga roots and shown to be a new cruciferous phytoalexin. Its chemical structure was proven by analysis of NMR spectroscopic data and chemical synthesis.