A Brief Review on Species Concepts with Emphasis on Plants

Species of all living organisms have been regarded as a basic unit of biodiversity. Regardless of the importance of its rank, the species is probably the most controversial taxonomic rank in biological science, and hence, there are over 30 concepts of species in use today. The earliest concept of species was the morphological species concept. Following Linnaeus, naturalists became aware that irrespective of the levels of morphological similarities among species, they occur as reproductively isolated entities in the field. This led to the biological species concept. The development of cladistic methods increased dissatisfaction with the biological concept of the species and led to the birth of the phylogenetic species concept. After discussing these three important concepts, I referred to other less widely used species concepts and to a study that presented a summary of 26 species concepts and to another study that discussed the species problem. All species concepts in current usage have limitations, and advantages and the proposition of many different species concepts lead to the conclusion that there is still no universally accepted definition of the taxonomic rank ‘species’. Any of these concepts can be suitable under appropriate circumstances, depending on the organism under study and the question that needs to be addressed. Variation in species concept among groups of organisms was also discussed with emphasis on plants, the vast majority of which belong to flowering plants category.