The Aizoaceae (ca. 2500 spp.) are a group of primarily succulent perennials whose center of diversity is southern Africa. In the broadest sense, the family consists of four primary lineages (recently retained at the rank of subfamily) which have previously been recognized at the rank of family: Aizoaceae (s.str.), Tetragoniaceae, Sesuviaceae, and Mesembryanthemaceae. The phylogenetic question regarding the sister group relationships among these primary lineages still has not been adequately resolved using morphological cladistic methodologies. Hypotheses have been put forth that either the Sesuvioideae is basal to the entire clade, or the Mesembryanthemoideae is basal. Some morphological characters support a Tetragonioideae + Aizooideae clade, however the relationship of this group to one of the others lacks similar support. To evaluate the phylogenetic relationships among these major lineages of the Aizoaceae, representative samples of Aizoon, Tetragonia, and Sesuvium were examined together with numerous samples from the "Mesembryanthemum" group, including taxa from both subfamilies Mesembryanthemoideae and Ruschioideae. Comparative sequencing of the rpl16 intron and other plastid regions was used to assess phylogeny within the family and to evaluate sister group relationships among the primary clades. Relative to outgroups from the Phytolaccaceae and Nyctaginaceae, the Aizoaceae were found to be monophyletic. The evolutionary relationships among the four major intrafamilial lineages (subfamilies) is examined with special reference to character changes in floral and fruit morphology and the evolution of succulence and xeromorphic adaptations in the Aizoaceae.

Key words: Aizoaceae, Caryophyllales, classification, molecular systematics, phylogeny, subfamilial relationships