"Phylogenetics" by Wiley (1981), p. 6
- A grouping of organisms given a proper name, or, a grouping that could be given a proper name but is not named as a matter of convention.
Glossary of "Cladistics (2nd ed.)" by Kitching et al. (1998)
- A named group of two or more organisms.
Glossary of Plant Systematics (1st ed.) by Simpson (2006)
- A group of organisms, ideally monophyletic and traditionally treated at a particular rank. Pl: taxa.
Glossary of "Life (9th ed.)" by Sadava et al. (2011)
Glossary of "Environmental Science: Earth as a Living Planet (2nd ed.)" by Botkin & Keller (1998)
- A grouping of organisms according to evolutionary relationships.
- 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.
- Kitching, I. J., Forey, P. L. Humphries, C. J. & Williams, D. M. 1998. Cladistics, 2nd ed.: the Theory and Practice of Parsimony Analysis. -xii + 228 pp. Oxford University Press, New York.
- Sadava, D., Hillis, D. M., Heller, H. C. & Berenbaum, M. R. 2011. Life: The Science of Biology, 9th ed. -xliv + 1266 pp. Sinauer Associates, Inc., Sunderland.
- Simpson, M. G. 2006. Plant Systematics. -xi + 590 pp. Elsevier Academic Press, Oxford.
- Wiley, E. O. 1981. Phylogenetics: the Theory and Practice of Phylogenetic Systematics. -xv + 439 pp. John Wiley & Sons, Inc., New York.