The vast majority of wasabi consumed in America is simply a mix of horseradish, hot mustard, and green dye,$4 from the American Chemical Society.
In fact, about 99% of all wasabi sold in the US is fake, $4 reports.
Even in Japan where most wasabi is grown, you won't have much better luck. Experts estimate that about 95% of wasabi sold in the country is an imitation.
True wasabi is difficult to grow and extraordinarily expensive, $4$4 at wholesale prices.
If you're eating real wasabi, you're consuming the stem of a plant, grated and pulverized into a spicy paste. It reportedly has a $4 taste, but needs to be eaten immediately - within 15 minutes, the freshly grated wasabi begins to lose its signature flavor.
Horseradish has a similar chemical makeup to wasabi, allowing it to mimic its spicy zing. The far-cheaper horseradish-based "wasabi" also has the added bonus of withstanding takeout sushi orders in a way that true, freshly grated wasabi could not.
Food fraud is a $4. In most cases, food scams aren't dangerous to consumers' health.