Arter av växter: Är de och vad är de?

The current confusion about what species are has two major causes. First, many authors discussing species concepts seem not to have considered for what purpose species are distinguished. Several proposed species concepts define species in a way that is only useful in a narrow field of advanced biological science. It is argued that species concepts should rather fulfil the needs of the majority of biologists who need species in order to communicate. Second, many species concepts (e.g. the biological and ecological species concepts) define species as die end products of certain specified speciation-processes, thereby confusing process and pattern and in a sense putting the cart before the horse. To facilitate unprejudiced studies of evolutionary processes it is argued that the species concept should be free from any assumptions about processes of speciation. Phylogenetic species concepts, stressing the importance of monophyly and defining species based on phylogenetic reconstructions only, are criticized for being of little use outside the field of phylogenetics. A species concept similar to Mallet's 'genotype-cluster definition', in which species are defined as groups of individuals within a discrete multi-character cluster of variation, is advocated. Whenever possible, characters should be chosen both from morphology and molecular markers, and, at least in critical taxa, the use of multivariate statistics to evaluate species distinctness is recommended. It is further argued that only those 'genotype clusters' that anyone has a practical need to distinguish should be formally recognised as taxa. In groups where many discrete genetical entities can be found, only those that are both morphologically readily distinguishable and have a unique ecology or distribution need to be recognised.