Wasabi (Wasabia japonica or Eutrema japonica), is a member of the Brassicaceae family that also includes cabbages, horseradish, and mustard.
It is also called Japanese horseradish, although it has absolutely nothing to do with horseradish at all but horseradish is often used as a complete substitute.
Wasabi’s stem is used as a condiment and has an extremely strong flavour. Its heat is more like a very hot mustard than that of the capsaicin in a chilli pepper, producing vapours that stimulate the nasal passages more than the tongue.
The plant grows naturally along stream beds in mountain river valleys in Japan. It is extremely difficult to cultivate and doesn’t store or travel well so real fresh wasabi is rare outside Japan and where it is available it is extremely expensive having been flown in overnight. The West is used to a blend of Wasabi with Horseradish and Mustard which this product is.
Because the burning sensations of Wasabi are not oil-based, they are short-lived compared to the effects of chilli peppers, and are washed away with more food or liquid. The sensation is felt primarily in the nasal passage and can be quite painful depending on the amount consumed.
True wasabi will contain wasabia japonica, while faux wasabi is or should be labelled Armoracia rusticana.