Bitter Lettuce (Sonchus oleraceus) , also known as common sowthistle, sow thistle, smooth sow thistle, annual sow thistle, hare's colwort, hare's thistle, milky tassel, milk thistle, soft thistle, or swinies, is scientifically classified as Kingdom: Plantae (unranked): Angiosperms (unranked): Eudicots (unranked): Asterids Order: Asterales Family: Asteraceae Tribe: Cichorieae Genus: Sonchus Species: S. oleraceus.