Hijiki is a kind of seaweed used for Nimono (food cooked in seasoned broth), salads and other dishes. Hijiki is usually black, short, thin sprouts, but long stems are also eaten sometimes. It is usually in dried form and needs to be re-hydrated before use.
Hijiki is full of nutrients like fiber, vitamins and minerals, especially having a lot of iron. If you are concerned about healthy eating, Hijiki may be the super vegetable (from the ocean) you are looking for. Interestingly, it also has a considerable amount of arsenic for a food, but it is widely eaten in Japan and is typically not a problem as long as you don’t eat excessive amounts.