The genus Packera
The largest tribe in Asteraceae, Senecioneae, is composed of about 150 genera and 3,500 species. Within Senecioneae, the genus Packera (subtribe Senecioninae), is composed of roughly 64 species with an unknown number of varieties . Packera was previously included in the genus Senecio as the informal group known as “aureoid senecios” by Asa Gray. They were then distinguished as the new genus Packera in 1975 by Á. Löve & D. Löve based on having different base chromosome numbers (x = 22, 23), various morphological differences, and molecular phylogeny data.
Ecologically, Packera is adapted to a variety of habitats. Some species are abundant and widely distributed, thriving in disturbed habitats. Others are narrow endemics, restricted to specialized habitats or are isolated on mountain tops. These restrictions have caused some species to be of conservation concern; others need further study to determine their conservation status.
Species boundaries in Packera are imprecise and taxonomy within Packera remains complex due to the species’ ability to easily hybridize, and because polyploidy is common throughout the genus, with roughly 40% of taxa being polyploids . Traits that distinguish Packera species and varieties are typically from differences in vegetative morphology or population-level differences in chromosome numbers . Otherwise, there is a lack in literature involving which particular character traits in Packera species are most influential in its history.
The overall goal of my dissertation is to obtain a better understanding of the evolutionary history and species relationships within the genus Packera. I plan to address this goal with three aims:
Obtain a general understanding of Packera’s evolutionary relationships by generating a robust nuclear and plastid phylogeny, as well as estimating its age.
Investigate the causes and consequences of both nuclear-nuclear and nuclear-plastid discordance, including evolutionary processes of incomplete lineage sorting (ILS) and gene flow, to understand how they influence the phylogenetic patterns seen in Packera.
Generate a new and revised probe set that better enriches for targeted genes with low paralogy to better handle complex groups in Asteraceae dealing with polyploidy.
This project also aims to address broader questions that can be applicable to other fields of biology, such as:
What role does polyploidy play in speciation events?
Are there common causes of discordance in phylogenies?
How does accounting for paralogy influence phylogenies and our understanding of these results?
Packera is a good model system to address these questions in complicated taxa given how some Packera species carry certain, distinguishable traits while others do not, some are widespread whereas others are endemic to restricted areas, and polyploidy, hybridization, and introgression are common within the genus.
PACKERA WEBSITE COMING SOON!!
As I continue my research on Packera, I thought it would be helpful to make this new information more accessible to everybody. So, as I keep finding more information throughout my dissertation, I will keep building this new website. If there are any questions or input you would like to have on this upcoming website, please contact me here.
Compositae Working Group (CWG) (2021). Global Compositae Database. Packera Á.Löve & D.Löve. Accessed at: https://www.compositae.org/aphia.php?p=taxdetails&id=1075407 on 2021-10-02
Trock, Debra K. (2006). Packera in Flora of North America. Vol. 20, Oxford Univ. Press. Link
Bain, J. F., & Golden, J. L. (2000). A phylogeny of Packera (Senecioneae; Asteraceae) based on internal transcribed spacer region sequence data and a broad sampling of outgroups. Molecular Phylogenetics and Evolution, 16(3), 331–338. Link
Barkley, T. M. (1988). Variation among the Aureoid Senecios of North America: a geohistorical interpretation. The Botanical Review, 54(1), 82. Link