Canola plant

Wild B. rapa (subspecies sylvestris L.) is regarded as the species from which the ssp. rapa (cultivated turnip) and oleifera (turnip rape) originated. It is native throughout Europe, Russia, central Asia and the Near East, with Europe proposed as one centre of origin. There is some debate as to whether the Asian and Near Eastern types arose from an independent centre of origin in Afghanistan and then moved eastward as B. rapa became domesticated. Prakash and Hinata (1980) suggest that oleiferous B. rapa subspecies developed in two places, giving rise to two different races, one European and the other Asian. 

Typically, B. rapa is found in coastal lowlands, high montane areas (the slopes of high valleys or mountain ranges), and alpine and high sierras. In Canada, where it is a recent introduction, it is found on disturbed land, typically in crops, fields and gardens, along roadsides, and on waste sites

Today, two species of Brassica have commercialized varieties with "double low" characteristics, i.e. low erucic acid content in the fatty acid profile and very low glucosinolate content in the meal, characteristics desirable for high-quality vegetable oil and high-quality animal feed.

In North America two species (B. napus and B. rapa) are considered to be of "canola" quality.

See also http://bch.cbd.int/database/record.shtml?documentid=12083 for information on B. napus