Testing the monophyly and position of the N orth A merican shrubby desert genus Leucophyllum ( S crophulariaceae: L eucophylleae)

L eucophyllum is one of the most remarkable endemic genera of N orth A merican deserts, with its simultaneous bloom of showy purple flowers. With E remogeton and probably C apraria it forms part of tribe Leucophylleae. L eucophyllum has 16 species distributed mostly throughout the C hihuahuan and T ehuacán deserts. The three genera were sampled to investigate the phylogenetic relationships among them and to test the monophyly of L eucophyllum , based on plastid DNA ( trnL‐ F , rps16 ) and nuclear ribosomal (nr) DNA ( internal transcribed spacer ) sequences. B ayesian inference and maximum‐likelihood analyses confirmed that tribe L eucophylleae is monophyletic and formed by the three Neotropical genera. Separate (plastid DNA and nr DNA ) and combined analyses retrieved L eucophyllum as paraphyletic, with L . mojinense as the sister species to the rest of the species in the tribe and C apraria spp. nested in one of two clades of L eucophyllum . Further monographic work is needed to identify the defining characters and limits of the genera, but we suggest that L . mojinense , with its different vegetative architecture, distinctive flowers and dissimilar distribution could be placed in its own genus. Each of the two clades in L eucophyllum could be considered a genus in its own right, and C apraria and E remogeton can be recognized as independent genera, as they are at present. L eucophyllum ambiguum , the type species of the genus, belongs to one of the clades so the species of the other could be considered members of a new genus. The only diagnostic character detected at present is a ventricose corolla tube in one of the clades in L eucophyllum and a pressed corolla tube in the other. © 2013 The Linnean Society of London