Variation in habit and a bewildering array of floral and fruit forms has likely contributed to making Capparaceae a ‘trash basket’ family. Recent phylogenetic analyses based on chloroplast sequence data indicate Capparaceae are paraphyletic with the monophyletic subfamily Cleomoideae more closely related to Brassicaceae then to subfamily Capparoideae (Capparaceae). Capparoideae also form a monophyletic clade with the exclusion of an anomalous genus, Forchhammeria. Although this genus is clearly placed outside the Capparaceae and Brassicaceae lineage, the precise relationship of Forchhammeria among other core Brassicales is unresolved. Forchhammeria (ten species) is endemic to the New World and has been placed in the tribe Stixeae along with Asiatic genera Stixis (seven species), Tirania (one species), and Neothorelia (one species) based on the floral characteristic of the unusual merosity number of six for Capparaceae (typically tetramerous). The goal of this study was to clarify the placement of the tribe Stixeae, especially the genus Forchhammeria, within the core Brassicales by using evidence from DNA sequences of rbcL, ndhF, trnL-trnF and matK. We were able to get DNA materials of almost all species of Forchhammeria and the genus Tirania. We sampled broadly within Capparaceae, Cleomaceae, and Brassicaceae as well as closely related families including Gyrostemonaceae, Resedaceae, Pentadiplandraceae, and Tovariaceae. These data indicate Tirania and Forchhammeria are most closely related to Gyrostemonaceae and Resedaceae. The phylogeny is used to assess floral character evolution as well as the evolution of dioecy among the core Brassicales.

Key words: Brassicales, Capparaceae, chloroplast DNA, Forchhammeria, phylogenetics