Caryophyllales have long been recognized as a natural assemblage (e.g., Braun 1864; Eichler 1875-1878). Previous circumscriptions based on morphological and embryological characters recognized up to nine families, and subsequent classifications that pioneered the use of chemical and anatomical characters included 12 families (e.g., Dahlgren 1975, 1980; Takhtajan 1980; Cronquist 1981; Thorne 1983, 1992a, 1992b). These circumscriptions remained largely intact for the past 30 years until recently when molecular phylogenetic analyses started reshaping concepts of Caryophyllales. Most notable is the discovery that certain carnivorous plants—the sundews and Venus flytrap (Droseraceae) and Old World pitcher plants (Nepenthaceae)—are closely related to Cronquist’s Caryophyllidae (Albert et al. 1992; Chase et al. 1993; Williams et al. 1994; Meimberg et al. 2000; Cuénoud et al. 2002). In addition, many families previously considered distantly related to Caryophyllales have been found to form a large clade with Caryophyllales (e.g., Asteropeiaceae and Physenaceae, Morton et al. 1997; Rhabdodendraceae, Fay et al. 1997a; Simmondsiaceae, e.g., D. Soltis et al. 2000). The strong support for this clade in recent multigene analyses (e.g., D. Soltis et al. 2000; Cuénoud et al. 2002) has led to a revised—and broader—circumscription of Caryophyllales by APG (1998) and APG II (2003).
Because of the potential confusion introduced by applying the name Caryophyllales to a large clade, not all investigators have accepted this circumscription. For example, Judd et al. (2002) continue to use Caryophyllales in a narrow sense (= core Caryophyllales in APG and APG II) and refer to the larger, more inclusive clade as the caryophyllid clade. Although morphological and anatomical characters are generally consistent with these expanded circumscriptions, nonDNA synapomorphies for this newly recognized expanded Caryophyllales have not yet been discovered. Caryophyllales sensu APG II (2003) comprise 29 families, including Caryophyllaceae, Nyctaginaceae, Phytolaccaceae, Aizoaceae, Amaranthaceae (including Chenopodiaceae), Molluginaceae, Basellaceae, Cactaceae, Didiereaceae, a polyphyletic “Portulacaceae” and several small families, some of them of problematic placement, such as Frankeniaceae, Tamaricaceae, Asteropeiaceae, Rhabdodendraceae, Simmondsiaceae, Nepenthaceae and Droseraceae. Two other families have been proposed: “Agdestidaceae” and “Petiveriaceae”.