Glossary of "The Evolution of Plants (2nd ed.)" by Willis & McElwain (2014)
- A relationship between individuals in which both species benefit.
Glossary of "Environmental Science: Earth as a Living Planet (2nd ed.)" by Botkin & Keller (1998)
- Relationships that exist between different organisms that are mutually beneficial.
- Botkin, D. B. & Keller, E. A. 1998. Environmental Science: Earth as a Living Planet, 2nd ed. -xxxxii + 649 pp. John Wiley & Sons, Inc., New York.
- Willis, K. J. & McElwain, J. C. 2014. The Evolution of Plants, 2nd ed. -ix + 398 pp. Oxford University Press, Oxford.