Coincya is a genus of flowering plant that belongs to the family Brassicaceae and is endemic to the British Isles. Only three species of plant belong to the genus, these being Coincya wrightii (Lundy Cabbage), Coincya cheiranthus (nokkasinapit) and Coincya monensis, which has two subspecies, C. monensis subsp. monensis (Isle of Man cabbage) and C. monensis subsp. recurvata (Star mustard).
The star mustard, a plant introduced to eight U.S. states is the same species as the Isle of Man cabbage but a different subspecies. It may have been introduced to the U.S. as the Isle of Man cabbage and subsequently evolved through the founder effect and geographic isolation into a new subspecies.