Eutrema wasabi.

Botanical name: 

Eutrema wasabi Maxim. Cruciferae. Japanese Horseradish.

Japan. This is Japanese horseradish, which grows wild on the coast and is cultivated in small quantities, rasped and eaten with fish. The best roots are cultivated only in clear spring water running down the mountain valleys.

Sturtevant's Edible Plants of the World, 1919, was edited by U. P. Hedrick.