An Aum is a plant that has the appearance of a droopy red & white flower with a green stalk. It is commonly found underneath Witchwood Trees and are often used in the creation of restoration spells.
Aum can only be found under Witchwood Trees, which are fairly frequent in forest biomes but can also spawn in other biomes. For the most part, a Witchwood tree will be surrounded by anywhere from 0 to 2 aums. While unlikely, it is possible for more to spawn. The only effective way to farm Aums is to farm Witchwood Trees, which are very picky in their growth requirements.