rbcL sequences support exclusion of Retzia, Desfontainia, and Nicodemia from the Gentianales

The taxonomic positions of Retzia, Desfontainia, and Nicodemia have been much discussed, and all three genera have been included in Loganiaceae (Gentianales). We have made a cladistic analysis of rbcL gene sequences to determine the relationships of these taxa to Gentianales. Four new rbcL sequences are presented; i.e., of Retzia, Desfontainia, Diervilla (Caprifoliaceae), and Euthystachys (Stilbaceae). Our results show that Retzia, Desfontainia, and Nicodemia are not closely related to Loganiaceae or the Gentianales. Retzia is most closely related to Euthystachys and is better included in Stilbaceae. The positions of Desfontainia and Nicodemia are not settled, but Desfontainia shows affinity for the Dipsacales s.l. and Nicodemia for the Lamiales s.l.