Wakame is an edible seaweed used in Japanese cooking and is typically available in dried and cut form (shown) in the U.S. but it can be found fresh in some Japanese markets. The seaweed is almost black in color with a nutty, briney smell.
To use dried wakame, rinse it with cool water then soak it in a bowl of warm water for about 5 - 10 minutes until it's soft. Once hydrated you can use it with rice or add it to soups and tofu dishes.
Is there a good substitute for wakame? If you don't have wakame then there is one alternative which is: