I just want to mention some of the Asian brasscias:
Bok Choy / Pak Choi Brassica rapa var. chinensis
Gai Lan "Chinese Kale/Brocoli" Brassica oleracea
Komatsuna "Spinach Mustard" Brassica rapa
and an Italian heirloom:
Spigariello Liscia / Broccolo Spigariello Brassica oleracea var. 'Spigariello'
One vendor told me that all Brassicas are insect-pollinated, and they all cross-pollinate, requiring a separation distance of ⅓ mile (the foraging range of some insects).