Perennial.
Mitsuba is, as the name indicates, an herb of Japanese extraction. It is said to have a flavor rather like parsley (which it physically resembles), but somewhat milder (though others say it is like Angelica). One blogger described the taste so: "Subtle. Maybe just a little nutty. Fresh. Maybe a little celery orientation. The herb is listed as Japanese Parsley, or Japanese Chervil, so that gives a good hint as to the flavor it imparts to foods." Though the plant's stems are cooked in the Orient for special uses (such as tying up sushi rolls), in western cuisine what's wanted is the leaves--used raw, not cooked into dishes, as cooking destroys the flavor (as with chervil).
