Mutualism is an obligated interaction. Synergism is another name for this type of plant co-operation. There are many different types of mutualism.
Inhabitational mutualism is when one mutualist lives within another.
Exhabitational mutualism is when the organisms involved are relatively independent physically, but interact directly. Indirect mutualism is the interaction among a set of species to modify the environment. Mutualism can either be symbiotic, nonsymbiotic, or facultative. Symbiotic mutualism is a relationship between different organisms live in direct contact, in which one or both benefit and at least one member of the pair cannot live an independent life without the other. Mutualism is a type of species interaction.