Cirsium (i.e., “thistles”) are one of the most taxonomically challenging groups of Compositae in North America. This study represents the first attempt to infer a broadly sampled phylogeny of Cirsium in North America. The two main objectives are to: (i) test whether currently hypothesized species variety complexes (C. arizonicum, C. clavatum, C. eatonii, and C. scariosum) constitute monophyletic lineages, and (ii) recircumscribe any taxa that are identified as problematic. Phylogeny reconstructions based on DNA sequence data from two nuclear ribosomal regions and four plastid markers were used to infer evolutionary lineages and test species’ delimitations. Eight species varietal complexes were resolved as polyphyletic. We recircumscribed these complexes and in doing so found evidence to support the recognition of six new taxa. We hypothesize that the extensive taxonomic difficulty within Cirsium is the result of several factors: (i) previously undescribed taxa, (ii) inadequate representation of taxa from herbarium specimens, (iii) phenotypic convergence, (iv) hybridization, and (v) incipient speciation. While we can provide evidence to support the recircumscription of some taxa, others remain unresolved. Therefore, we are working on a phylogenomic study of North American Cirsium to answer remaining taxonomic questions as well as provide a robust framework for biogeographic studies.

中文翻译：

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蓟是一团糟：解开北美蓟属（Cardueae：Compositae）的分类

Cirsium（即“蓟”）是北美菊科植物分类学上最具挑战性的类群之一。这项研究代表了首次尝试推断北美 Cirsium 的广泛采样系统发育。两个主要目标是：(i) 测试当前假设的物种多样性复合体（C. arizonicum、C. clavatum、C.eatonii 和 C.scariosum）是否构成单系谱系，以及 (ii) 重新界定任何被确定为有问题。基于来自两个核核糖体区域和四个质体标记的 DNA 序列数据的系统发育重建用于推断进化谱系和测试物种的定界。八种品种复合体被解析为多系。我们重新界定了这些复合体，并在此过程中找到了支持识别六个新分类群的证据。我们假设 Cirsium 中广泛的分类学困难是几个因素的结果：（i）以前未描述的分类群，（ii）植物标本馆标本中分类群的代表性不足，（iii）表型收敛，（iv）杂交，以及（v）初期物种形成。虽然我们可以提供证据支持重新界定某些分类群，但其他分类群仍未解决。因此，我们正在对北美 Cirsium 进行系统发育研究，以回答剩余的分类学问题，并为生物地理学研究提供一个强大的框架。虽然我们可以提供证据支持重新界定某些分类群，但其他分类群仍未解决。因此，我们正在对北美 Cirsium 进行系统发育研究，以回答剩余的分类学问题，并为生物地理学研究提供一个强大的框架。虽然我们可以提供证据支持重新界定某些分类群，但其他分类群仍未解决。因此，我们正在对北美 Cirsium 进行系统发育研究，以回答剩余的分类学问题，并为生物地理学研究提供一个强大的框架。