A southern European milk thistle, Silybum marianum, with white-blotched leaves.
Late 16th century; earliest use found in William Langham (fl. 1597), doctor and herbalist. In some forms from lady + thistle, perhaps originally reflecting a genitive compound with unmarked first element; it has been suggested that the plant was so called because the white spots on its leaves were popularly supposed to have been caused by the Virgin Mary's milk dripping on them, but there appears to be no early evidence from 16th- or 17th-cent. herbals to support this suggestion.