Complex sentence: It is also called Japanese horseradish, although horseradish is a different plant (which is often used as a substitute for wasabi), its stem is used as a condiment and has an extremely strong flavor.
Split into simpler sentences: It is also called Japanese horseradish, although horseradish is a different plant (which is often used as a substitute for wasabi). Its stem is used as a condiment and has an extremely strong flavor.