Species doesn't mean as much in the plant world. Cabbage, broccoli, cauliflower, kale, Brussels sprouts, collard greens, kohlrabi, and gai lan are all Brassica oleracea. You can have specimens that are even technically the same cultivar but wildly different alimentary character.
Hooray!! I totally love the way 'Brassica' vegetables provide such a vivid illustration of the amazing variety that some selection-pressure can yield on the development of essentially a single type of input organism. Makes you wonder what might happen when these types of selection-pressures start affecting humankind more!
Brassica and domesticated dogs diversified because of controlled breeding. Unless you get a bunch of totalitarian eugenicists with differing goals, I dont know how this could happen with people.
Oh yeah. Brassica rapa has your turnip, napa cabbage, bok choy and rapini/rabes. Brassica napus gives canola oil, swedish turnip, and rutabaga. Mustard comes from B. juncea, B. nigra and B. hirta.
Also those species names aren't really even guaranteed to be accurate because biologists, botanists, geneticists, etc, can't even really agree on where to draw the line.
There's a whole genre of Brassica memes and it's fantastic.
