Morphometrics of Daucus (Apiaceae): A counterpart to a phylogenomic study

Authors: ARBIZU, CARLOS - University Of Wisconsin; REITSMA, KATHLEEN - Iowa State University; Simon, Philipp; Spooner, David

Submitted to: American Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2014
Publication Date: 11/12/2014
Publication URL: http://handle.nal.usda.gov/10113/60050
Citation: Arbizu, C., Reitsma, K.R., Simon, P.W., Spooner, D.M. 2014. Morphometrics of Daucus (Apiaceae): A counterpart to a phylogenomic study. American Journal of Botany. 101(11):2005-2016.

Interpretive Summary: Cultivated carrot, technically referred to as Daucus carota, is the most widely grown crop of the carrot family and is cultivated on 1.1 million hectares globally of which 35,000 hectares are US grown and worth $600M annually. Cultivated carrot was selected from the common weed, Queen Anne’s Lace, which is widely distributed across temperate regions of the globe. This study reevaluated what is a good species in the genus Daucus, through an examination of the form of the plant, or a morphological study, It is a companion study of the same populations that examined what is a good species through the use of DNA characters. We examined these populations for 40 morphological characters (such as leaf or stem or seed sizes and shapes) from 80 populations of 14 species of Daucus and nine species in related genera that were not classified as Daucus. All measurements were made from plants grown from seed in an experimental garden plot in Ames Iowa where the national seed collections of Daucus species are maintained. Most of these 40 morphological characters showed tremendous variation. A computer-assisted analysis of these data distinguished most species well but some species could not be so easily distinguished. In most cases, those species that were hard to distinguish had similar problems with the DNA data. This study helps to better identify the US collection of wild and cultivated carrots, shows us cases where additional studies are needed to define some species, and guides carrot breeders and other users of these collections into the choice of collections for their studies.

Technical Abstract: Molecular phylogenetics of genome-scale data sets (phylogenomics) often produces phylogenetic trees with unprecedented resolution. A companion phylogenomics analysis of Daucus (carrots) using 94 conserved nuclear orthologs supported many of the traditional species but showed unexpected results that require morphological analyses to make sense of the phylogenomics results. We examined character state distributions, stepwise discriminant analyses, canonical variates analyses, and hierarchical cluster analyses from 40 morphological characters from 80 accessions of 14 taxa of Daucus and nine species in related genera in an experimental plot. Most characters showed tremendous variation with character state overlap across many taxa. Multivariate analyses separated the outgroup taxa easily from the Daucus ingroup. Concordant with molecular analyses, most species form phenetic groups, but problems are shown in the recognition of 1) the subspecies of D. carota and D. capillifolius 2) D. sahariensis and D. syrticus and 3) D. broteri and D. guttatus. Phenetic analyses, in combination with molecular data, support many Daucus species, but mostly by overlapping ranges of size and meristic variation. Daucus capillifolius and the subspecies of D. carota are poorly separated morphologically, are paraphyletic, and all could be recognized at the subspecies rank under D. carota. Daucus sahariensis and D. syrticus are so similar morphologically that they could be placed in synonymy. The status of D. broteri and D. guttatus is unresolved, with the present data supporting three species. These data help to better classify the germplasm collections of these important genetic resources, and guide breeders and other users into the choice of germplasm for their applied studies.