Origin and evolution of the South American endemic Artemisia species (Asteraceae): evidence from molecular phylogeny, ribosomal DNA and genome size data Jaume Pellicer A,B,F , Teresa Garnatje C , Julián Molero A , Fatima Pustahija D,E , Sonja Siljak-Yakovlev D and Joan Vallès A A Laboratori de Botànica, Facultat de Farmàcia, Universitat de Barcelona, Avinguda Joan XXIII s/n, 08028 Barcelona, Catalonia, Spain. B Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB, United Kingdom. C Institut Botànic de Barcelona (CSIC-ICUB), Passeig del Migdia s/n, Parc de Montjuïc, 08038 Barcelona, Catalonia, Spain. D Ecologie, Systématique, Evolution, UMR CNRS 8079, Université Paris-Sud, Bâtiment 360, 91405 Orsay Cedex, France. E Faculty of Forestry, University of Sarajevo, Zagrebacka 20, 71000 Sarajevo, Bosnia and Herzegovina. F Corresponding author. Email: jaumepellicer@ub.edu Abstract. Genus Artemisia is thought to have reached the Americas across the Bering Strait from Asia during the late Tertiary, but the systematic position of the South American endemic species and the migration routes towards the south have not yet been studied. We used nuclear DNA sequences to unravel the interspecific relationships among the South American Artemisia and their connections with the remaining species of the genus, as well as using fluorescent in situ hybridisation and genome size assessments to characterise this polyploid complex. Most of the species are clustered in a monophyletic clade, nested within the American endemic clade, with the exception of A. magellanica Sch. Bip., which appears segregated from the other American species and constitutes a clade together with A. biennis Willd. Fluorescent in situ hybridisation and genome size data revealed that monoploid genome size remains quite constant across ploidy levels and a proportional increase of ribosomal loci was detected, a dynamic not usually found in this genus. The results are discussed in the light of evolutionary processes which occur in plants, and plausible origins for the South American endemic species are hypothesised. Introduction Artemisia L. (Asteraceae, Anthemideae) is a genus of worldwide distribution, growing in the temperate zones of the northern hemisphere, with a few species spread across the southern hemisphere (Bremer and Humphries 1993; Oberprieler et al. 2009). There are existing hypotheses regarding the mechanisms and migration pathways followed by Artemisia in colonising new habitats. On the one hand, the Asian species belonging to the subgenus Seriphidium have been suggested as possible ancestors of the North American endemic Artemisia and a likely migration pathway across the Bering Strait has been highlighted (Ling 1991, 1995). On the other hand, McArthur and Plummer (1978) and McArthur et al.(1981), although agreeing with this migration route, proposed that the herbaceous members of the subgenus Artemisia could have been differentiated in North America during the Pleistocene in response to climatic changes, giving rise to the species of the subgenus Tridentatae and other endemics. The origin of the Tridentatae from subgenus Artemisia is also supported by Jeffrey (1995) on the basis of phytochemical data. The South American endemic Artemisia species occur mainly in Argentina (Ariza 1997), some of them reaching Chile (Zuloaga et al. 2008), where they have been traditionally used in medicine (Roig 2002; and references therein). Studies devoted to elucidating the molecular systematics of this complex of species are still lacking, and the role they play in the diversification of the genus is of special interest. In addition, global taxonomic treatments of Artemisia that include the South American species are scarce. The exception is A. mendozana DC., which was assigned to the subgenus Seriphidium by Candolle (1837) and later renamed as Seriphidium mendozanum by Bremer and Humphries (1993) in their revision of the Anthemideae, without taking into account the opinions of Roig and Ambrosetti (1989) who reported the presence of heterogamous capitula in the species. This complex is composed of perennial shrubs or subshrubs. In the case of A. magellanica Sch. Bip., although being described as perennial (Cabrera 1971; Ariza 1997), it has also been reported to behave as a biennial/perennial herb (J. Molero, pers. obs.). As mentioned before, this complex of species is of particular interest for the evolutionary history of the genus because of their geographical distribution and the scarcity of Artemisia taxa in the southern hemisphere. A phylogenetic circumscription of these species within the genus might shed light on their origin and the CSIRO PUBLISHING www.publish.csiro.au/journals/ajb Australian Journal of Botany, 2010, 58, 605–616 Ó CSIRO 2010 10.1071/BT10047 0067-1924/10/070605