Horseradish

From AoCWiki

Horseradish is a Tradeskill Resource used in crafting the alchemical concoctions [Sharphowler Steak], [Old Mordant], [Sagebark Tea], [Bearbreaker Stew], [Wildwood Heart], and [Augerwine].

It can be purchased from the vendors in Purple Lotus Swamp, Lacheish Plains, or Poitain.