THE SPECIES CONCEPT IN QUERCUS

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Abstract
Summary: The modern biological species‐concept, defined by genetic isolation, describes a phyletically independent system of populations. Most of the species‐concepts in everyday use for the oaks (Quercus) exhibit genetic interchange with other so‐called species. Nevertheless, these classical concepts remain in use and represent biologically meaningful populations. In addition, it is suggested that the classical species of Quercus may represent phyletic units in species‐grade evolutionary advances. A comparison between the biological species‐concept and the classical species‐concept in Quercus suggests why the classical concepts have been retained. The biological species‐concept appears to be a population system of extraordinary complexity and difficult to delimit in Quercus. This genetically isolated complex population system is not directly comparable to genetically discrete species in most other genera. The prime function of the species binomial is as a unit of communication. The biological species‐concept must be used with greater flexibility as regards taxonomic rank if its designation by means of a binomial cannot provide a functional information retrieval system.