A systematic analysis of Heliotropiaceae (Boraginales) based on trnL and ITS1 sequence data

The infrafamilial relationships of Heliotropiaceae (Boraginaceae subfam. Heliotropioideae according to traditional systems) are reevaluated using molecular data of nuclear ITS1 (86 species) and plastidal trn LUAA intron (66 species) sequences. The results obtained from our investigations show that traditional generic limits warrant adjustment. Heliotropiaceae fall into two large clades. The first clade includes, in basal position, the genus Ixorhea . The genus Myriopus (formerly Tournefortia sect. Cyphocyema) is sister to Euploca (formerly Hilgeria, Schleidenia, Heliotropium sect. Orthostachys). The remaining sections of Heliotropium, Tournefortia sect. Tournefortia and the three small genera Argusia, Ceballosia, and Nogalia, segregated from Heliotropium, constitute the second large clade. Argusia, Ceballosia, and Nogalia cluster within clades of Heliotropium and therefore are reincluded in this genus. Within Heliotropium, the species of former Tournefortia sect. Tournefortia represent a lineage of tropical New World Heliotropium species, growing in humid environments, whereas all other Heliotropium species are found in semi-arid habitats. Before new combinations in the genus Heliotropium are made for "Tournefortia", the exact relationship within New World Heliotropium needs to be resolved, and a revision of "Tournefortia" is inevitable. We advocate maintaining the genus Tournefortia, which is easily defined, and we conclude that under this definition the genus Heliotropium is paraphyletic. Five genera are thus accepted; 22 new combinations within Heliotropiaceae are presented.