Molecular systematics of Cardamine and allied genera (Brassicaceae): Its and non-coding chloroplast DNA

Representatives of the genera Cardamine, Dentaria, Nasturtium, Rorippa and Armoracia (Brassicaceae) were analyzed to elucidate their phylogenetic rela tionships based on nuclear (ITS) and non-coding chloroplast (cp) DNA sequen ces. Dentaria seems to be polyphyletic. The two studied Dentaria species gr oup with different Cardamine clades, and it is argued that D. bulbifera is an allopolyploid originating from a hybridization between a Cardamine and a Dentaria species. In the ITS tree, Nasturtium and Rorippa form well suppor ted clades but their relationship to Cardamine and Armoracia remains unreso lved, in the cpDNA tree, Nasturtium groups together with Cardamine. Hybridi zation events apparently played a role in the evolution of Nasturtium. The Cardamine/Nasturtium clade is separated from a clade placing Rorippa and Ar moracia together. Armoracia is closely related to Rorippa. Analyses of the 19 Cardamine species studied revealed three main groupings, a northern hemi spheric and two southern hemispheric groups. Within the northern hemisphere taxa the C. pratensis complex forms a well supported clade which seems to be closely related to C, amara, C. raphanifolia and C, flexuosa. The positi ons of C. hirsuta and C. impatiens are uncertain. The two southern hemisphe re clades consist of New Guinean species and south-eastern Australian/Tasma nian and subantarctic species, respectively. They may reflect migration rou tes from the northern to the southern hemisphere, but further studies are n ecessary to fully understand the evolution of the bihemispheric distributio n pattern of Cardamine.