Pacific Coast Iris species delimitation using three species definitions: biological, phylogenetic and genealogical

Abstract

Morphological characters are used to discriminate the five Oregon species of the Pacific Coast irises (Iris series Californicae). In nearly every case, fixed differences were found between species, revealing that they are good phylogenetic species. However, when the biological species concept is applied, the whole series is found to be one biological species. Sequence data were generated from the chloroplast DNA region between the atpbeta and rbcL genes. For this 700 bp region, the maximum divergence observed in the series was one percent. These sequences, together with three restriction site characters, were used to produce a cladogram for multiple individuals of all species in the group. On the resulting consensus cladogram, the different individuals from each species do not cluster together. This could result from either introgressive hybridization or the retention of ancestral polymorphism. When the genealogical species concept is applied, only one species can be identified: the whole Series Californicae. There are therefore two natural levels at which taxa can be defined. It is recommended that the phylogenetic species be used as the taxonomic species in this group.Copyright 1998 The Linnean Society of London