Thanks for all replies. Unfortunately this is my first attempt to
gardening and I'm unable to compare things yet. This plant tastes very well and it is very possible that this is Arugula, however I have no idea how it could get into place where I have sown kale seeds. I do have arugula's seeds, and I did sown them, but in another raised bed, in one of the square foot square. Anyway, it looks like a very tasty surprise and I will definitely not remove it. The question however is - where is my kale now?
I also sowed quite a few plant seed that I have never planted before and now I dont know if what I see growing is weeds or what I planted.
That's exacly how I feel - even notes and labels are not helping, but I assume it is a part of the fun and of a learning curve.