Molecular systematics of the New Zealand Pachycladon (Brassicaceae) complex: Generic circumscription and relationships to Arabidopsis sens. lat. and Arabis sens. lat.

Abstract

Nuclear ribosomal DNA ITS sequence data were used to assess the relationships of Cheesemania, Ischnocarpus, and Pachycladon to each other and to other genera in the Brassicaceae. Phylogenetic analyses are congruent with other studies that infer the Pachycladon complex (including Pachycladon, Cheesemania, and Ischnocarpus) is monophyletic. The complex occurs within an Arabidopsoid clade that includes Arabidopsis and the recently recognised segregate genera Beringia, Crucihimalaya, Olimarabidopsis, and Pseudoarabidopsis, and the Arabis segregates Boechera and Turritis. The Pachycladon complex is sister to Beringia and Crucihimalaya, and forms a distinct New Zealand lineage. Molecular clock estimates suggest the Pachycladon complex diverged from its nearest relatives between 1.0 and 3.5 million years ago. The close relationship of Cheesemania, Ischnocarpus, and Pachycladon is reflected in low (<2.6%) sequence divergence values, high bootstrap support (98%), and the lack of a well‐resolved topology in the phylogenetic trees. Morphological characters and data from previous studies of intergeneric hybrids and DNA Amplified Fragment Length Polymorphisms, support the recircumscription of Pachycladon to include species placed in Cheesemania and Ischnocarpus. New combinations are made in Pachycladon for species previously placed in Cheesemania and Ischnocarpus. A new name, P. cheesemanii, is presented for Ischnocarpus novae‐zelandiae as that species epithet is preoccupied in Pachycladon.

Keywords:

• Brassicaceae
• Pachycladon
• Cheesemania
• Ischnocarpus
• Arabis
• Arabidopsis
• phylogeny
• New Zealand flora