Flowering Siberian Kale.
Kale
Brassica oleracea
Most kales are Brassica oleracea, and will cross with other members of this species such as broccoli, cabbage, cauliflower, and collards.
There is one exception, Siberian Kale, which is Brassica napus -it will not cross with members of the B. oleracea family but will cross with rutabagas and rape.