Mizuna is a very interesting vegetable.  It tastes like a cross between mustard and arugula.  The leaves are serrated and contain high content of chlorophyll.  They're very popular in Japan.  They leaves are great in salads becuase of their spicy flavor.  They will do best in cooler climate, so start them during the Spring or Fall.  Space them about at least 1 foot apart for best results.