RESEARCH PAPER An Andean radiation: polyploidy in the tree genus Polylepis (Rosaceae, Sanguisorbeae) A. N. Schmidt-Lebuhn 1,2 , J. Fuchs 3 , D. Hertel 4 , H. Hirsch 1 , J. Toivonen 5,6 & M. Kessler 2 1 Abteilung Pflanzeno ¨ kologie, Institut fu ¨ r Biologie, Martin-Luther-Universita ¨ t Halle-Wittenberg, Halle, Germany 2 Institute for Systematic Botany, University of Zu ¨ rich, Zu ¨ rich, Switzerland 3 Abteilung Cytogenetik und Genomanalyse, Leibniz-Institut fu ¨ r Pflanzengenetik und Kulturpflanzenforschung Gatersleben (IPK), Gatersleben, Germany 4 Abteilung O ¨ kologie und O ¨ kosystemforschung, Albrecht-von-Haller-Institut fu ¨ r Pflanzenwissenschaften, Georg-August-Universita ¨t Go ¨ ttingen, Go ¨ ttingen, Germany 5 Abteilung Systematische Botanik, Albrecht-von-Haller-Institut fu ¨ r Pflanzenwissenschaften, Georg-August-Universita ¨t Go ¨ ttingen, Go ¨ ttingen, Germany 6 Section of Biodiversity and Environmental Science, Department of Biology, University of Turku, Turku, Finland INTRODUCTION The Andes are one of the global centres of plant diversity and endemism (Myers et al. 2000; Barthlott et al. 2007). The Andean uplift started about 20 Mya (Burnham & Graham 1999) but alpine habitats at and above the tree- line are fairly young, dating from the Pliocene (Gregory- Wodzicki 2000). Yet these biomes are home to some of the most impressive plant radiations on Earth (Linder 2008), including Lupinus (81 spp., Hughes & Eastwood 2006), Gentianella (170 spp., von Hagen & Kadereit 2001), Valeriana (160 spp., Bell & Donoghue 2005), Eric- aceae (800 spp., Luteyn 2002), and Calceolaria (230 spp., Molau 1988). The processes that lead to these radiations presumably include adaptive shifts to new high-elevation habitats as these became available during orogeny, isola- tion of organisms on different mountain ranges and slopes, and range shifts due to past climatic fluctuations (Hooghiemstra & Van der Hammen 2004; Brumfield & Edwards 2007). At the same time, because of their young age, many species in these radiations are rather ill defined, with hybridisation and introgression being com- monly inferred from morphology. As such, the mecha- nisms leading both to the diversification of the taxa as well as to maintenance of species identities are of interest. Polylepis (Rosaceae, Sanguisorbeae) is a genus of about 15–30 wind-pollinated tree and shrub species growing at high elevations in the Andes from Venezuela to Argentina (Bitter 1911; Simpson 1979; Kessler 1995a,c; Kessler & Schmidt-Lebuhn 2006). Polylepis is ecologically important Keywords Cell size; chromosome; flow cytometry; genome size; guard cell size; ploidy. Correspondence A. N. Schmidt-Lebuhn, Institute for Systematic Botany, University of Zu ¨ rich, Zollikerstrasse 107, CH-8008 Zu ¨ rich, Switzerland. E-mail: schmidtleb@yahoo.de Editor S. Graham Received: 5 February 2009; Accepted: 1 November 2009 doi:10.1111/j.1438-8677.2009.00297.x ABSTRACT The Andean tree genus Polylepis (Rosaceae) is notorious for the high mor- phological plasticity of its species and the difficulty in their circumscription. The evolutionary mechanisms that have driven diversification of the genus are still poorly understood, with factors as diverse as ecological specialisa- tion, reticulate evolution, polyploidisation and apomixis being proposed to contribute. In the present study, chromosome counts, flow cytometry and stomata guard cell size measurements were employed to document for the first time the presence of polyploidy in the genus and to infer ploidy levels for most species. Inferred ploidy levels show a clear progression from dip- loidy in cloud forest species to polyploidy (tetra- to octoploidy) in the mor- phologically and ecologically specialised incana group, indicating that polyploidisation may have played a major role in speciation processes and the colonisation of novel habitats during the Andean uplift. At least two species of Polylepis comprise populations with varying degrees of ploidy. More extensive studies are needed to obtain a better understanding of the prevalence and effects of intraspecific polyploidy in the genus. Plant Biology ISSN 1435-8603 Plant Biology ª 2010 German Botanical Society and The Royal Botanical Society of the Netherlands 1