In the leaf pouches of  H. physophora lies the extrafloral nectaries,  where ants can get the nectar that was created by the plant, it can be viewed as parasitism by the ants, but the plant benefits immensely from the presence of ants as well.
Also located in the leaf pouches are extrafloral nectaries, which provide the ants with nectar made by the plant, and also some food bodies that provide the ants with further nutrition as they mature to become foragers and insect predators. So far this looks like simple parasitism by the ants, as if they simply take advantage of the plant for food and shelter. However, the plant also benefits greatly from this relationship. It forms an association with the ant species, Allomerus decemarticulatus. 
