Boondoggled by sushi houses.

Learn something new every day... Today: most wasabi isn't wasabi.

The truth is, what passes for wasabi in the U.S., in all but the most rarified temples of Japanese cuisine, is a mixture of ordinary western horseradish (Armoracia rusticana), Chinese mustard, cornstarch and green food coloring. The mixture reasonably approximates its cousin, Wasabia japonica, a difficult-to-grow and therefore very pricey gourmet condiment. Even when you buy imported Japanese "wasabi" in a tin of powder or a tube of paste, provenance does not guarantee authenticity. In fact, a good rule of thumb is: most wasabi isn't, and many products claiming to contain wasabi don't.

The Nibble :: Real Wasabi - Authentic Japanese Wasabi Powder (Wasabia Japonica)