Original: Even in Japan , horseradish dyed green is often substituted for the more expensive wasabi traditionally served with sushi . The Japanese botanical name for horseradish is seiyÅ wasabi , or '' Western wasabi '' .
Simplified: Horseradish is similar to wasabi , so in many places and restaurants , they use horseradish as wasabi , as it is much cheaper than wasabi , which is very expensive .