Close association of two individuals belonging to different species resulting in advantages for both partners.

In the english literature, the term "symbiosis" is often used in its neutral meaning (close association). In this case, the term "mutualistic" is added, when both partners obtain advantages from the association. In cases, when one partner is living within the other, the term "endosymbiosis" is used. Well-known examples for (mutualistic) symbioses are lichens (see figure), mycorrhizal symbioses, or root nodules.