They leaves are more wrinkled and crinkled than I'm used to, but it could well be a Brassica rapa or Brassica oleracea.
To me it is "funny looking" for Bok Choy because it seems to lack the celery-like stalks. I've only grown smooth-leaved, shiny-leaf B. rapas. And not many Chinese cabbages to maturity!
Can you rule out some kind of Kale or Western cabbage? Mustard? A nibble would reveal "mustard". I guess it isn't comfry or chard.
Are the leaves hairy? They look kind of fuzzy and thick, not shiny like I expect. In Chinese cabbage, I expect most of each leaf to be thin and only the veins to be thick.
It could be a youngish Michihli Chinese cabbage that has not had time to form a very compact had. But unusually wrinkled leaves. It doesn't look like ANY Napa Chinese cabbage I've seen a photo of.
Or one of many other B. rapa varieties, assuming those exist in heavily wrinkled and crinkled forms.
Sorry I can't narrow it down.
The thing is, Brassica vegetables are very flexible, and have been so selected and crossed over centuries that you can get almost any appearance within one species. Once you've said "It is a B. rapa of some kind", after that, it's pretty much "what you see is what you got".
It's disturbing to me, but the various breeding lines not only diverged into different forms like Bok Choy, tatsoi, Napa cabbage and Michihli cabbage, those lines then also some CONVERGED so that two B. rapa vegetables may look very similar and yet have very different great-great-grandparents! Or two fairly closely-related B. rapas can look very different. So useful names are mostly based on appearance, not genetics.
"What you see is what you got".
If you're sure they came from a seed packet and are not weeds, you might as well boil or stir-fry and eat some. Unless someone has seen that specific kind-of-loose-headed and-very-wrinkled variety, it'll be hard to say what it is.
For even more head-spinning genetics, Google "brassica rapa triangle of u".
Some think that three "ancestral" Brassica species formed inter-species hybrids long ago, creating three other Brassica species:
Theoretically ancestral species:
Brassica rapa (syn. Brassica campestris) – turnip, Chinese cabbage, Bok Choy, tatsoi
Brassica nigra – Black mustard
Brassica oleracea – cabbage, kale, broccoli, Brussel sprouts, cauliflower
Theoretically inter-species hybrid species:
Brassica juncea – Indian mustard
Brassica napus – Rapeseed, rutabaga
Brassica carinata – Ethiopian mustard
I recently bought some seeds named "Mizunarubasoi" because they are a recently stabilised hybrid of:
a cold-tolerant Mizuna (B. rapa Japonica Group),
Maruba santoh (B. rapa Pekinensis Group, a loose head type Chinese cabbage)
and tatsoi (B. rapa Chinesis Group")
Once they did DNA sequence comparisons, the nomenclature specialists deleted all naming categories other than "B. rapa". (There used to be names like "Brassica rapa Chinesis Group" for Bok Choy and "Brassica rapa (Pekinensis Group) for Napa, Michihli and other Chinese cabbages).
Now there is only "B. rapa" and what the kids in the street call things. Thanks, scientists!!
Their theory is that names should ONLY reflect ancestry, and if gardeners need to distinguish among Bok Choy, tatsoi, Michihli, komatusna and whatever, that is just their problem. They won't allow accepted scientific binomial nomenclature to be useful for anything but indicating actual ancestry. And they keep changing their minds.
That also means that even if you took your plant to a CSI lab and asked for a complete genetic sequence, probably all THEY could say would "B. rapa" ... or it might be "B. oleracea". To narrow it down farther, they would have to compare your plant with possible matches. The gene lines are so interwoven within each Brassica species, DNA tests would be like a paternity test where every suspect shared many grandparents with every other suspect.
