Phylogeny, biogeography, systematics and taxonomy of Salicornioideae (Amaranthaceae/Chenopodiaceae) – A cosmopolitan, highly specialized hygrohalophyte lineage dating back to the Oligocene

Abstract Salicornioideae (Amaranthaceae / Chenopodiaceae) comprise 11 genera and ca. 100 species of succulent halophytes distributed worldwide in coastal and inland saline habitats. Most species have peculiar articulated, seemingly leafless stems and spike‐like sessile thyrses with highly reduced flowers hidden by fleshy bracts. We analysed sequence data of four markers (ETS, ITS, atpB‐rbcL, matK‐trnK ) from 57 species, 9 subspecies, 1 variety and 2 hybrids representing all curently accepted genera using maximum likelihood, Bayesian analysis, fossil‐calibrated molecular dating and ancestral area analysis. All molecular markers gave similar phylogenetic signals. Salicornioideae probably originated in Eurasia during the late Eocene–early Oligocene. The divergence of the early main clades took place in the middle Oligocene with the separation of Allenrolfea /Heterostachys, Halocnemum /Halopeplis /Halostachys /Kalidium and Arthrocnemum /Microcnemum /Tecticornia /Salicornia / Sarcocornia lineages. The latter lineage diversified most and comprises ¾ of the species of the subfamily. The Arthrocnemum macrostachyum /Microcnemum lineage diverged at the turn of the Oligocene/Miocene – while the Arthrocnemum subterminale, Tecticornia and Salicornia /Sarcocornia lineages were all present by the middle Miocene. Long‐distance dispersal has taken place several times to the Americas ( Allenrolfea /Heterostachys, Arthrocnemum subterminale, Salicornia /Sarcocornia ), South Africa ( Halopeplis, Salicornia /Sarcocornia ) and Australia ( Tecticornia, Salicornia /Sarcocornia ). Most currently accepted genera were resolved as monophyletic. However, Sarcocornia is paraphyletic in relation to Salicornia, and Arthrocnemum proved to be polyphyletic. In addition, the name Arthrocnemum is a nomenclatural synonym of Salicornia. As a consequence, we propose the merging of Sarcocornia under Salicornia and provide 19 new nomenclatural combinations and one replacement name. For Salicornia (incl. Sarcocornia ) we propose a new infrageneric classification to accommodate the four phylogenetically and geographically well‐supported sublineages of the genus. We also propose abandoning the name Arthrocnemum in its current use, and describe two new genera, Arthrocaulon (Eurasia, Africa) and Arthroceras (North America), and provide three new nomenclatural combinations.