Looks like baby bok choy. This and various other similar leafy vegetables are garden forms of mustard plants. So when they mature and bloom you get mustard flowers, regardless of what the plant looks like. Cabbage, cauliflower, kale and so on ... all mustards. Of course the more extremely divergent (unnatural) kinds may not been seen flowering.

Thanks!

If you let those flowers mature into pods, you can harvest the seeds when they're dry & brown - that's what I do