A LOCAL FLORA AND THE BIOLOGICAL SPECIES CONCEPT

Up to the end of the 19th century the typological species concept was universally accepted, in which degree of morphological difference was the species criterion. This concept was increasingly replaced (particularly in zoology) beginning around 1900 by the biological species concept because the criterion of morphological distinctness broke down in the case of sibling species and of highly distinct intrapopulational variants. The yardstick for the recognition of biological species is the noninterbreeding of coexisting species in a local situation. This yardstick can be applied to isolated populations only by inference. It is discussed whether the making of such inferences is too arbitrary to be acceptable. A local flora is analyzed to determine whether polyploidy, apomixis, hybridization, and other deviations from regular sexual reproduction are sufficiently frequent in plants to make the biological species concept illusory. It is found that the number of difficulties is small, validating use of the sympatric situation as yardstick for the ranking of allopatric populations.