There are two types of B. napus: 1) oil-yielding oleiferous rape,
of which one subset with specific quality characteristics is often
referred to as "canola" (vernacular name), and 2) the tuber-bearing
swede or rutabaga.
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=9845
for information on B. rapa