Rue (Ruta graveolens) is a hardy evergreen subshrub of the citrus family, prized for its intensely bitter, musky-pungent blue-green foliage. Once a staple of European and Mediterranean kitchens and apothecaries, it survives today as a sparingly used seasoning in Ethiopian and a few Italian dishes — and as a caution, since contact with the plant can blister the skin.