Roman writers, e.g. Columella in AD 42, distinguished between two main types of turnips: ‘napus’, which was relatively slender, pointed, and delicate; and ‘rapa’, which was large and round. Ever since, there has been confusion over how to classify turnips. The current arrangement is to call the common white turnip B. rapa; to assign its relatives the swede and rutabaga to B. napus ssp rapifera; and rape, grown for its oil-bearing seeds, to B. napus. But this is not universally agreed.