Systematic relationships of New Zealand endemic Brassicaceae inferred from nrDNA ITS sequence data

Abstract

Phylogenetic relationships of New Zealand species of Brassicaceae belonging to the South Island endemic Ischnocarpus, Iti, Notothlaspi, and Pachycladon, and the indigenous Cardamine, Cheesemania, Lepidium, and Rorippa were studied using nuclear ribosomal internal transcribed spacer sequences. Results support a monophyletic Notothlaspi and suggest that species of this genus are not closely related to Thlaspi, the genus to which Hooker provisionally assigned N. australe. The cosmopolitan genus Cardamine is paraphyletic by the inclusion of the monotypic genus Iti. The association of Iti with New Zealand Cardamine is of particular significance, as the relationships of this monotypic genus have historically proven elusive. Cheesemania species, Ischnocarpus novae-zelandiae, and Pachycladon novae-zelandiae form a closely related monophyletic group. The species of Lepidium form a monophyletic group, but the New Zealand species are not monophyletic indicating two possible dispersal events to New Zealand. Additionally, the tribes Arabidieae, Lepidieae, and Sisymbrieae are polyphyletic. This study highlights the difficulty of using traditional characters such as fruit type and cotyledon arrangement to define the tribes of the Brassicaceae.