Numerical taxonomy

Numerical taxonomy is a classification system in biological systematics which deals with the grouping by numerical methods of taxonomic units based on their character states.. It aims to create a taxonomy using numeric algorithms like cluster analysis. The concept was first developed by Robert R. Sokal & Peter H.A. Sneath in 1963 and later elaborated by the same authors. Phenetics is a closely related discipline and draws heavily from the methods of numerical taxonomy.

Although intended as an objective classification method, in practice the choice and weighing of morphological characteristics is often guided by available methods and research interests. Furthermore, the general consensus has become that the taxonomic classification should reflect evolutionary (phylogenetic) processes. Some connections between phylogenetic trees and the spectral decomposition of the variance-covariance matrix of quantitative traits subject to Brownian motion over time have been established , providing a theoretical link between phylogenetic methods and numerical taxonomy. The specific phenetic algorithms proposed in numerical taxonomy, however, often fail to properly reconstruct the phylogenetic history of organsims.

Numerical taxonomy remains useful in cases where biological species concepts can not be applied, e. g. clonal evolution as in apomictic microspecies like blackberries.