I've pulled up one or two of these so far this summer, and this evening I decided on a whim to try tasting it, as it didn't look like a normal weed and seemed to keep growing back in the same place. It was really tasty - slightly sweet at first and then it becomes peppery like arugula. I don't know what to compare it to, but I'm really interested to know what it is. I looked through about a thousand Google Image search results for edible plants in Iowa but didn't see anything like this. Any ideas?

In addition to the photo of the leaves from above, I can say that it grows in a small clump of 25-30 of these leaves, all flat and growing outward to form a circle. I pulled up the whole thing before deciding to taste one of them. They pull off the roots really easily. I'm not sure what the roots look like because I don't know yet if I want this one gone!

Thanks for any help you can provide!