According to Johnny's Seed Company (where I order a lot of my seeds) :
"Mizuna produces dozens of pencil thin white stalks with deeply cut, fringed leaves."The pencil thin stalks are apparent in the picture above, as well as variation in leaf shape. There have been quite a lot of oval mizuna leaves. So many that a few days ago I couldn't figure out what kind of green someone was asking me about. Perhaps this is because it is still pretty warm out, or maybe mizuna just has a variety of leaf shapes.