Cladogenesis and reticulation in Cuscuta sect. Denticulatae (Convolvulaceae)
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ORIGINAL ARTICLE
Cladogenesis and reticulation in Cuscuta sect. Denticulatae (Convolvulaceae) Miguel A. García 1,2
&
Saša Stefanović 1 & Catherine Weiner 3 & Magdalena Olszewski 3 & Mihai Costea 3
Received: 5 May 2018 / Accepted: 11 October 2018 / Published online: 28 October 2018 # The Author(s) 2018
Abstract As traditionally circumscribed, Cuscuta sect. Denticulatae is a group of three parasitic plant species native to the deserts of Western USA (Cuscuta denticulata, Cuscuta nevadensis) and the central region of Baja California, Mexico (Cuscuta veatchii). Molecular phylogenetic studies confirmed the monophyly of this group and suggested that the disjunct C. veatchii is a hybrid between the other two species. However, the limited sampling left the possibility of alternative biological and methodological explanations. We expanded our sampling to multiple individuals of all the species collected from across their entire geographical ranges. Sequence data from the nuclear and plastid regions were used to reconstruct the phylogeny and find out if the topological conflict was maintained. We obtained karyotype information from multiple individuals, investigated the morphological variation of the group thorough morphometric analyses, and compiled data on ecology, host range, and geographical distribution. Our results confirmed that C. veatchii is an allotetraploid. Furthermore, we found previously unknown autotetraploid population of C. denticulata, and we describe a new hybrid species, Cuscuta psorothamnensis. We suggest that this newly discovered natural hybrid is resulting from an independent (and probably more recent) hybridization event between the same diploid parental species as those of C. veatchii. All the polyploids showed host shift associated with hybridization and/or polyploidy and are found growing on hosts that are rarely or never frequented by their diploid progenitors. The great potential of this group as a model to study host shift in parasitic plants associated with recurrent allopolyploidy is discussed. Keywords Host shift . Host range . Hybridization . Polyploidy . Parasitic plant . Speciation
Introduction Cuscuta (dodders) is a plant genus of nearly 200 species of stem parasites (Yuncker 1932; García et al. 2014; Costea et al. 2015a) that has evolved within Convolvulaceae (reviewed by Stefanović and Olmstead 2004, 2005). The genus is nearly Miguel A. García and Saša Stefanović contributed equally to this work. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13127-018-0383-5) contains supplementary material, which is available to authorized users. * Miguel A. García [email protected] 1
Department of Biology, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada
2
Royal Botanic Gardens Kew, Richmond, Surrey TW9 3AE, UK
3
Department of Biology, Wilfrid Laurier University, Waterloo, ON N2L3C5, Canada
cosmopolitan but the majority of species are native to North and South America, belonging to Cuscuta subg. Grammica, the largest inf
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