This study highlights the potential for complicated patterns of genetic variation relative to cytotypic variation and provides evidence for the role of cytotypic variation and geographic isolation in shaping diversity, differentiation, and potentially speciation in the P. amabilis-P. woodhousei complex.

No abstract

Encelia, Enceliopsis, and Geraea are three closely related genera of shrubs and herbs distributed in the arid lands of western North and South America. Resolution of relationships within Encelia has traditionally been difficult because there is some morphological overlap among species, and species hybridize when sympatric. In this study, we used DNA sequence data from two nuclear regions (ITS and ETS) and two chloroplast regions (psbA-trnH and trnS-trnfM) to infer phylogenetic relationships among 19 species, subspecies, and varieties of Encelia. Eight species of Enceliopsis, Geraea, Simsia, and Bahiopsis were also included as outgroups. These data support previous hypotheses suggesting that Encelia is monophyletic and sister to Enceliopsis + Geraea. In addition, our data provide evidence for two major subclades within Encelia that are supported by morphological synapomorphies. However, little differentiation was observed among species of Encelia within subclades. This lack of differentiation may be the result of a recent diversification of the genus including recent radiation in the Peninsular Desert.

Patterns of woody-plant mortality often reflect tradeoffs associated with resource allocation. Plants that allocate a high proportion of carbon acquired from photosynthesis to non-structural carbohydrate storage may be buffered from the synergistic effects of climate change and episodic disturbance.

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.