The plant prefers growing in cold water.
It has large, thick, dark brown leaves. The leaves are cut into thin strands when being processed, and turn even darker – to black in fact — when cooked or dried.
In Japan, it is harvested on the Ise peninsula on the east coast of Japan.
If fresh, just wash and use.
If dried, rinse, then soak for 15 minutes in cold water to let it rehydrate. Squeeze dry, then use as directed in recipe. If you are making a soup, you can add some of the water you soaked it in for the soup.
Store dried in a sealed container in a cool area indefinitely.
Store fresh or cooked in the refrigerator, and use up within a few days.