Subspecies Variation of Daucus carota Coastal (“Gummifer”) Morphotypes (Apiaceae) Using Genotyping-by-Sequencing

Abstract

Abstract—The genus Daucus is widely distributed worldwide, but with a concentration of diversity in the Mediterranean Region. The D. carota complex presents the greatest taxonomic problems in the genus. We focus on a distinctive phenotypic group of coastal morphotypes of D. carota, strictly confined to the margins to within about 0.5 km of the Mediterranean Sea and the Atlantic Ocean, which we here refer to as coastal morphotypes or D. carota subsp. “gummifer” complex. They are loosely morphologically coherent, sharing a relatively short stature, thick, broad, sometimes highly glossy leaf segments, and usually flat or convex fruiting umbels. We analyzed 288 accessions obtained from genebanks in England, France, and the USA, and an expedition to Spain in 2016, covering the Mediterranean and Atlantic coasts and Balearic Islands, where much of the gummifer complex variation occurs. Our study includes 112 accessions not examined before in this context. Genotyping-by-sequencing identified 29,041 filtered SNPs. Based on high bootstrap support from maximum likelihood and Structure analysis we highlight three main clades. The gummifer morphotypes are intercalated with members of Daucus carota subspecies carota and subspecies maximus in two of these main clades, including a clade containing accessions from Tunisia (also including D. carota subsp. capillifolius) and a clade containing accessions from western Europe (including the British Isles), southern Europe (including the Balearic Islands and the Iberian Peninsula) and Morocco. These results support five independent selections of the gummifer morphotypes in these restricted maritime environments in the Mediterranean and nearby Atlantic coasts. Daucus annuus (=Tornabenea annua) and Daucus tenuissimus (=Tornabenea tenuissima) also fall firmly within D. carota, supporting their classification as morphologically well-defined subspecies of D. carota, which are accepted here under the new combinations Daucus carota subsp. annuus and D. carota subsp. tenuissimus, respectively. Types are indicated for most of treated names, including designation of four lectotypes and three epitypes, which fix their further use.