Physiological race

In biological taxonomy, race is an informal rank in the taxonomic hierarchy, below the level of subspecies. It has been used as a higher rank than strain, with several strains making up one race. Various definitions exist. Races may be genetically distinct phenotypic populations of interbreeding individuals within the same species, or they may be defined in other ways, e.g. geographically, or physiologically.Genetic isolation between races is not complete, but genetic differences may have accumulated that are not (yet) sufficient to separate species.

In botany, the Latin words stirps and proles were traditionally used, and proles was recommended in the first botanical Code of Nomenclature, published in 1868.

Races are defined according to any identifiable characteristic, including gene frequencies. "Race differences are relative, not absolute". Adaptive differences that distinguish races can accumulate even with substantial gene flow and clinal (rather than discrete) habitat variation.

In botany, where physiological race (mostly used in mycology), biological race, and biological form have been used synonymously, a physiological race is essentially the same classification as a forma specialis, except the latter is used as part of the infraspecific scientific name (and follows Latin-based scientific naming conventions), inserted after the interpolation "f. sp.", as in "Puccinia graminis f. sp. avenae"; while the name of a race is added after the binomial scientific name (and may be arbitrary, e.g. an alphanumeric code, usually with the word "race"): "Podosphaera xanthii race S".

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