Setchellanthaceae (Capparales), a new family for a relictual, glucosinolate-producing endemic of the Mexican deserts

Setchellanthus caeruleus Brandegee is a rare microphyllous shrub, densely p ubescent with T-shaped Malpighian hairs, with many stamens, 5-7 free blue t o lilac petals, an elongate, 3-carpellate, deeply trisulcate ovary with axi le placentation and proto-parietal vasculature, and a straight embryo essen tially lacking endosperm. It is known only from two widely disjunct areas i n the Chihuahuan and Tehuacan deserts of northern and south-central Mexico. The genus was named for phycologist W. A. Setchell (1864-1963; a biographi cal note is included). Its taxonomy, morphology, and geography are outlined , and the results of four associated papers on flower and seed anatomy, veg etative anatomy, pollen structure, and nucleotide sequence of the rbcL gene are discussed. The species is so highly distinct in its relatively primiti ve morphology and chemistry that it is here placed into its own, newly esta blished monotypic family near the Caricaceae and Moringaceae and basal to t he core group of glucosinolate (mustard oil) producing families (but less b asal than, e.g., Bretschneideraceae, Akaniaceae, and Tropaeolaceae). The ne w evidence supports Dahlgren's reclassification of an expanded order Cappar ales.