Sesuvium and Cypselea are closely related succulent genera within the Sesuvioideae (Aizoaceae). Since Cypselea is nested in Sesuvium in molecular studies and both genera share traits separating them from other members of the subfamily, we propose to include Cypselea in Sesuvium. Sesuvium (incl. Cypselea) comprises 14 species and is distributed worldwide with centres of diversity in southern Africa and North and Central America. Sesuvium comprises erect to procumbent herbs with opposite leaves that often bear conspicuous sheath-like lateral appendages on the petioles (pseudostipules). These and the many-seeded capsules are diagnostic traits, separating Sesuvium from the closely related genera Trianthema and Zaleya. Sesuvium is usually found in coastal or otherwise saline areas and is phylogenetically divided into an African (5 spp.) and an American lineage (9 spp.). While all African species are C4 plants, the American lineage also comprises a derived C3 lineage, which includes the cosmopolitan species S. portulacastrum. Some floras provide descriptions and keys for locally relevant species, but currently no comprehensive taxonomic treatment is available for Sesuvium. In this paper, a key and descriptions for all species are provided. Furthermore, we compile information on the rare and poorly known species of the genus and address issues concerning species concepts in Sesuvium, which impede species identification. The inclusion of Cypselea in Sesuvium leads to three new combinations: Sesuvium humifusum , Sesuvium mezianum and Sesuvium rubriflorum .