Integrating DNA barcode data in a monographic study of Convolvulus
Williams BRM., Mitchell TC., Wood JRI., Harris DJ., Scotland RW., Carine MA.
© International Association for Plant Taxonomy (IAPT) 2014. The stage at which DNA sequence data is incorporated into the taxonomic process and the extent of its contribution has been much discussed, but rarely in the context of assembling a taxonomic revision or monograph of a sizeable group of organisms. We present a new approach, the “foundation monograph”, which incorporates DNA sequence data into a large taxonomic study in a fast and pragmatic way, thereby overhauling the taxonomy of species-rich, problematic plant groups. In this pilot study we focus on Convolvulus and use this group to exemplify how DNA barcode data can be utilised in the production of a “foundation monograph”. DNA was extracted from 310 accessions, representing 140 species, most of which (285) were herbarium specimens. Samples were sequenced for the proposed plant barcoding markers rbcL, matK and ITS. Sequencing success for each marker was 74%, 49% and 63% respectively. Of the 189 species of Convolvulus recognized to date, 74% (140 species) were sampled and 68% (128 species) were successfully sequenced for at least one region. Specimen age did not impact sequencing success except in the case of matK, the longest region. Eighty percent of the species sampled exhibited combined rbcL + matK barcodes not shared with another species. The addition of ITS increased this proportion to 99%. Phylogenetic analyses of the chloroplast (152 accessions representing 90 Convolvulus species) and nuclear (200 accessions representing 112 Convolvulus species) datasets both resulted in a well-resolved and well-supported topology, and revealed four main clades with strong geographical signal. Convolvulus appeared as paraphyletic with respect to Calystegia. Species limits of eight species complexes in which morphological delimitation proved difficult and for which multiple accessions were obtained were evaluated using the phylogenetic framework as a basis. Our study highlights the utility of herbarium specimens as a source of material for DNA extractions as well as the utility of DNA barcode data in the production of a “foundation monograph”, while also providing a robust, well-sampled and well-supported framework within which generic relationships, character evolution and biogeography can be investigated.