A Phylogeny for the African Restionaceae and New Perspectives on Morphology’s Role in Generating Complete Species Phylogenies for Large Clades

Abstract

Difficulties with obtaining complete species‐level phylogenies include (1) the accurate identification and sampling of species, (2) obtaining a complete species sampling, and (3) resolving relationships among closely related species. We addressed these in a study of 317 species and subspecies of the African Restionaceae. Accurate species identification and collection in the field was facilitated by a morphology‐based interactive key to all species. Despite intensive fieldwork, however, material for DNA extraction could not be obtained for 20 of the 292 species of the focal Restio subclade. Furthermore, the 6831 aligned nucleotides and 1685 parsimony‐informative sequence characters were insufficient to resolve relationships fully within the clade. A simulation indicated that an additional 5000–7000 bases may have been needed to achieve supported resolution in the neighborhood of 95%–100%. Instead of further sequencing, we investigated the phylogenetic utility of the large set of characters contained within the interactive key data set, exploiting recent advances in parsimony and Bayesian programs that allow multistate and supermultistate (including continuous for parsimony) morphological characters. On doing so, parsimony resolution increased 17% to nearly 100%, and overall support increased in both parsimony (bootstrap) and Bayesian (posterior probability) frameworks. Taxa for which DNA data were lacking could be placed in fully resolved positions. Experiments using the parsimony ratchet indicated that placement of these morphology‐only taxa may have been completely accurate 30% of the time, to within three nodes of accuracy 60% of time, and accurate to genus 96% of the time. Accurate placement of morphology‐only taxa through Bayesian analysis may require extensive effort devoted toward exploring tree and parameter space. We conclude that the increasingly available large morphological data sets associated with interactive keys or informatics initiatives represent convenient yet potentially powerful tools in overcoming many of the commonly encountered obstacles in molecular‐based species‐level phylogenetics.