Subspecies variation of Daucus carota coastal (“gummifer”) morphotypes (Apiaceae) using genotyping-by-sequencing

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, the earliest name for taxa in this group. 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
narrowly restricted maritime environments in the Mediterranean Region and
nearby Atlantic coasts. Daucus annuus (=Tornabenea annua) and Daucus
tenuissimus (=Tornabenea tenuissima; Cape Verde) also fall firmly within
Daucus carota, supporting their classification as morphologically
well-defined subspecies of D. carota, which are accepted here with new
combinations. Types are indicated for most of treated names, including
designation of four new lectotypes and two new epitypes, which contribute
to fixation of further use of these names.