Is horseradish and Wasabi the same thing?
They are different plants -- two different members of the mustard/cabbage family. Both have a similar sharp, pungent flavor and penetrating aroma, but wasabi is generally considered to be  more potent. In prepared form, horseradish is somewhat coarsely grated, while wasabi is ground to the finest possible paste. Some (but not all) cultivars of wasabi are green; for others, green coloring is often added during processing.