Irit

An Irit herb can be identified at level 40 herblore, and it is used to make super ani-poison potions and super strong anti-poison potions.

A popular method to obtain irit herbs is by killing chaos druids in Taverley Dungeon or in the wilderness part of the Edgeville Dungeon, just west of the level 10 thugs.

Alternatively, you can acquire a decent amount of irit leafs from the farming skill. To plant the seeds, you need 44 farming.