Enteromorpha compressa.
Botanical name:
Enteromorpha compressa (Linn.) Grev. Algae.
This is one of the edible seaweeds of Japan.
Sturtevant's Edible Plants of the World, 1919, was edited by U. P. Hedrick.
A herbal distance course
Henriette's herbal is one of the oldest and largest herbal medicine sites on the net. It's been online since 1995, and is run by Henriette Kress, a herbalist in Helsinki, Finland.