A fully resolved chloroplast phylogeny of the brassica crops and wild relatives (Brassicaceae: Brassiceae): Novel clades and potential taxonomic implications

Brassicas boast an enormous diversity of economically important products. Strikingly, relationships among main lineages are still unknown. The phylogeny of the tribe Brassiceae (Brassicaceae) was reconstructed for 89 species using four plastid regions (rpl32­trnL, atpI­atpH,psbD­trnT,ycf6­psbM). Representatives of almost all genera were sampled, covering the entire natural range of the tribe from Central Asia to the western Mediterranean, including four previously unsampled genera (Ammosperma,Eremophyton,Fezia,Pseudofortuynia). Phylogenetic analysis recovered eight well­supported clades in the tribe including a new African clade (Henophyton) comprised of genera that have not been previously sampled. Relationships within and between the eight major clades are strongly supported for the first time. The earliest­divergent lineages in the tribe are the clades Vella and Zilla. Henophyton is sister to the clade that includes the lineages Nigra, Crambe, Cakile, Savignya, and Oleracea. Core Brassiceae—a new clade defined here—is comprised of two subclades: (1) Nigra, Crambe, and Cakile and (2) Savignya and Oleracea. Within the Oleracea lineage, a new Core Oleracea clade is defined. Several genera were confirmed to be polyphyletic or paraphyletic, including Brassica, Erucastrum, Sinapis, Diplotaxis and Cakile. Economically important species belonging to the genera Brassica were primarily distributed across the two most species­rich lineages, Nigra or Oleracea. Collectively, the finding of these novel clades has numerous taxonomic implications.