Here is a brassica variety I don't recall seeing before. In Chinese, it is 鹤斗白 (hè dǒu bái, which is untranslatable into anything sensible*), but I have been unable to find a proper English name or a more specific scientific name. Each head is about the same size as what many of you call baby bok choy**.
鹤斗白
The leaves of this one are darker and curled and the whole head forms a sort of cup shape (which is the meaning of the second character.
I'll be having it with my dinner later and shall report on the taste.
* The name translates literally as 'crane (the bird) cup-shaped white)
** but the Chinese don't - it's called Shanghai greens here. Baby bok choy here is something different. See up thread.