The wasabi that comes in the form of a green paste and is commonly used as a condiment on sushi and other types of seafood is made of the wasabi plant. Since wasabi is difficult to cultivate, most wasabi in supermarkets and restaurants is merely colored horseradish.
Wasabi is grown in the mountain valleys of Japan alongside steam beds; however, even in ideal conditions, wasabi cultivation is quite difficult, especially on a large scale, which makes genuine wasabi such a rare treat. Wasabi plants are only grown in a few locations in Japan, and real wasabi plants are rare outside of Japan. Due to the high demand, a wasabi imitation is often produced using horseradish, mustard, starch and green food coloring to imitate the appearance of genuine wasabi.