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.

中文翻译：

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Cuscuta sect 的枝发生和网状形成。齿科（旋花科）

按照传统的界限，菟丝子教派。Denticulatae 是一组三种寄生植物物种，原产于美国西部沙漠（Cuscuta denticulata、Cuscuta nevadensis）和墨西哥下加利福尼亚州中部地区（Cuscuta veatchii）。分子系统发育研究证实了该组的单系性，并表明分离的 C. veatchii 是其他两个物种之间的杂种。然而，有限的抽样留下了替代生物学和方法学解释的可能性。我们将抽样范围扩大到从整个地理范围内收集的所有物种的多个个体。来自核和质体区域的序列数据用于重建系统发育并找出拓扑冲突是否保持。我们从多个个体中获得了核型信息，通过形态计量学分析研究了该群体的形态变异，并汇编了有关生态、寄主范围和地理分布的数据。我们的结果证实 C. veatchii 是异源四倍体。此外，我们发现了以前未知的 C. denticulata 的四倍体种群，我们描述了一个新的杂交物种，Cuscuta psorothamnensis。我们认为这种新发现的天然杂交种是由与 C. veatchii 相同的二倍体亲本物种之间的独立（可能是最近的）杂交事件产生的。所有多倍体都显示出与杂交和/或多倍体相关的宿主转移，并且发现它们生长在很少或从不经常被二倍体祖先光顾的宿主上。