Species Concepts and Problems in Practice: Insight from Botanical Monographs

monographs from three journals treating 1,790 species were surveyed to develop an overview of 1) species and infraspecific concepts used by monographers and 2) problems in species delimitation due to variation, hybridization, and asexual reproduction. Most monographers did not discuss species or infraspecific concepts; the majority of those who did used a morphological or taxonomic concept. Infraspecific categories, whether subspecies or varieties, were used by most monographers to delimit morphologically and geographically differentiated entities within species. About 7% of the species monographed were sufficiently variable that species delimitation was difficult and 10% were subdivided infraspecifically. About 12% were involved in hybridization, but in only about 1% was there sufficient complexity to make species delimitation problematic. These data are compared to the incidence of hybridization reported for the flora of the British Isles. About 5% of the species surveyed were hypothesized to be of hybrid origin. Asexual reproduction was a significant problem in monographs treating only two groups. These biological phenomena, partic- ularly hybridization and asexual reproduction, were distributed unevenly across the plant groups monographed, with most presenting few problems. Based on these results, it is argued that there are gaps between theoretical and practical work at the species level that should be bridged. It seems clear that monographers working with most groups need not be unduly concerned that the biological nature of the taxa they study makes them inappropriate for phylogenetic analyses or for the ap- plication of certain species concepts. On the other hand, difficult groups are equally important for understanding the patterns and processes of evolution and their special biological properties should be highlighted.