Mizuna is a Japanese mustard green. The word means “water vegetable” referring to the water retained in the juicy stalks. The leaves are feather shaped with a peppery taste. The green is frequently found in mesclun greens mix.
You can use mizuna as a salad green. We just pick off a few leaves at at time rather than harvesting the full head. It works equally as well in dishes that call for fresh arugula leaves like pastas and even casseroles.
Depending on your location this might be a difficult green to find. You can find it in some Asian grocery stores and some farmer's markets. It is quite easy to grow in the spring and summer. See instructions below.
You can plant seeds in early spring (after last frost) through summer then another crop in late summer to fall. Seeds should be planted 1" apart then thinned to every 6". Alternately you can purchase plant starts at the nursery then just space them 6" apart. The plants mature in 40-50 days.
You can harvest the individual leaves as needed or you can pull up the entire head.
This image shows small mizuna plants (about 6" tall) in raised garden bed with drip system for water. Image by: gourmetsleuth.com