Holland Greens (Brassica rapa 'Tyfon')
Yup, "mustard greens without the mustard". One of the breeding goals was "forage", and the total lack of mustard flavor means it can be fed to cows without making their milk taste weird.
I just found the seeds recently and haven't grown them out yet. Supposedly, they taste so mild that they take on the flavor of whatever you cook them with. They are also supposed to be good for 2-3 cuttings, but they are supposed to get hairy and tough when old. I don't know yet if the regrowth after a cutting is tough and hairy!
Someone else said "reasonably palatable ... by itself", but came out "tasting great" when cooked with other things, and "They make a good substitute for spinach"
http://blueboathome.com/blogs/...
These links are from the above article:
http://www.wisegeek.com/what-a...
http://www.recipetips.com/glos...
http://www.nicholsgardennurser...
https://www.superseeds.com/pro...
And they are supposed to grow so rapidly that "one row would feed the whole Red Army".
Maybe that would be true with the downsized Red Army, and a very, very long row!