But the source of the spiciness is the same, at least: https://en.wikipedia.org/wiki/Allyl_isothiocyanate

That's also true inside Japan. True wasabi is really hard to grow commercially and thus very expensive.

> 95% of the time the stuff with your sushi isn't wasabi

so unexpected that i had to look it up; turns out you're right: https://chefcoca.com/blogs/food-service-equipment-resources/...

Isn’t wasabi just horseradish. Are you saying the mustard is what makes it not true.

> Isn’t wasabi just horseradish

Wasabi and horseradish are different! Horseradish is used as a substitute for wasabi so widely that you definitely can get the impression they are the same. But they are different plants.