Nucleotide sequence of rbcL and phylogenetic relationships of Setchellanthus caeruleus (Setchellanthaceae)

The nucleotide sequence (1462 bases) from the chloroplast gene for the larg e subunit of ribulose-l, 5-bisphosphate carboxylase/oxygenase (rbcL) was ut ilised for the monotypic Mexican endemic genus Setchellanthus to assess its phylogenetic affinities. Phylogenetic analyses of rbcL sequence data robus tly group Setchellanthus with Other mustard oil producing plants included i n Dahlgren's expanded order Capparales. Within this assemblage, maximum par simony places Serchellanthus sister to a clade comprised of the North Ameri can family Limnanthaceae, the sister taxa Koeberlinia + Salvadora + Batis, and the core Capparales (Brassicaceae + Capparaceae, Gyrostemonaceae + Rese daceae, Pentadiplandraceae, and Tovariaceae). Maximum likelihood analyses r everse the relationship of Setchellanthus and Limnanthaceae, placing Setche llanthus sister to the Koeberlinia + Salvadora + Batis plus the core Cappar ales assemblage, with Limnanthaceae sister to these. The rbcL sequence of S etchellanthus possesses a putative stop codon ending at position 1440, twel ve bases beyond the 1428 site usual for dicots. This extended 3' terminus i s consistent within the expanded Capparales for a clade that comprises the above-named taxa. The position of Setchellanthus in the rbcL phylogram prov ides support for elevation of this unispecific genus to family rank, postul ated in view of its unique morphological characters.