XVI International Botanical Congess

Publications on species concepts have been increasing since 1950. The mainly one-sided definitions individually invoke only one or a few factors. The Òbiological species conceptÓ was influential in the past, but it will not work for pteridophytes. Other proposals involve geography, ecology, cytology, enzymology, and genomics Criteria are also derived from cladistics, so-called Òphylogenetic species.Ó But the traditional morphological methods of species discrimination are still viable. No one species concept is applicable to all situations. The various proposals are here criticized. I reach the conclusion that a synthetic method utilizing the preponderance of evidence is the most defensible route for delimiting species. Taxonomists should take a multifaceted approach, a global species concept.