Systematic research has undergone a great deal of change and evolution throughout the past several decades. What was once informed by primarily morphological information has largely switched to being guided by a variety of molecular data – whether micro-satellites, Sanger Sequencing, or high-throughput methods such as target-capture/enrichment. These tools have revolutionized the field rightfully so, but incorporating other data sources (particularly morphological and ecological) along with physical experimentation (primarily through greenhouses) remain a vital means of understanding the many lineages we have uncovered through the aforementioned means.

As such, we should strive to take wholistic approaches to identifying and characterizing the taxa we ultimately recognize taxonomically. Genetic work provides a less subjective view of our organisms’ evolutionary history and genetics interactions (or the lack of such) than the subjective interpretation of variable morphological features but can benefit greatly from morphometric comparisons that identify features of interest for distinguishing between taxa. This further permits the production of data-informed dichotomous keys for field biologists and naturalists to identify different species/varieties, making the research more practically useful for a wider audience. These, combined with ecological/geographical approaches (whether niche modeling/comparisons in environmental space or extensive field work to characterize substrate types, vegetation communities, and successional stages) ultimately aids in recognizing species which may potentially be at risk of local extirpation or complete extinction even. Coalescing this information with greenhouse experiments can further highlight whether species are capable of selfing or hybridizing and the implications of such on a given taxon’s potential genetic diversity in the field.

While each component is important, molecular phylogenetics provides the most robust evidence for delimiting relationships among and within species. Shortcomings of general phylogenetics have been noted – including issues of incomplete lineage sorting, introgression, insufficient resolution, organellar (especially chloroplast) capture, recombination, and others – but are all factors accounted for when possible. For morphologically variable and intergrading groups, exemplified by the perennial taxa of Heterotheca, morphological interpretations are important considerations but should be viewed in light of high-throughput phylogenetic results. As the variation within many species can seem to exceed the variation amongst them, phylogenetics is our best guide to understanding relationships among these morphologically complex organisms.

As such, several tools are employed to develop a revised and data-driven taxonomy for Heterotheca. Molecular phylogenetic data, throughout a combination of HybSeq (exon capture or target-capture/enrichment) and RADseq, are the principle drivers elucidating evolutionary relationships, hybridization or introgression, and polyploidization events both throughout the genus and within select species complexes. Analyzing these data through bioinformatic means will reveal the complicated natural histories of numerous species complexes and help determine what species or varieties (and how they are defined) should be recognized. A variety of concatenation and coalescent methods for trees and networks will be utilized to establish the origins of putative hybrids and reconstruct polyplpoidization events in the genus’ collective diversification.

Morphometric comparisons of key characters, including leaf dimensions and involucre properties, will further help determine which characters are consistent or more variable for recognizing various taxa. Due to the highly variable nature of populations within numerous species complexes, having objective measurements and statistical differences will provide firmer grounds for deciding how is best to treat these difficulty to characterize or identify species/varieties. Generating illustrations and photographs of these differences, particularly since glandularity and vestiture have been important factors, will further prove important for communicating these differences to other biologists and naturalists alike.

Characterization of given species’ niches and distributions will further be undertaken at a variety of scales. This work is largely dependent upon natural history (herbarium) collections and recent observations (primarily through iNaturalist) to locate regions where members of given species complexes can be found. Climatic comparisons and niche/distribution modeling may distinguish among closely-related species’ niches in addition to local characterizations through years in the field. Extensive field work – particularly in the desert/intermontane regions of the southwest, southern/central Rocky Mountain, and the Great Plains – has further helped understand not only the substrate specificity of various taxa but also the plant communities associated with species of interest.

Greenhouse and breeding experiments lastly will help evaluate the capacity of different species/varieties to hybridize or introgress. Thorough breeding experiments have only thus far been published for the H. subaxillaris complex, leaving much to learn about the reproductive systems of other species. The capacity for various species to self, and whether the triploids and tetraploids are of auto- or allo-polyploid origin, remains unknown for most taxa. Generating F1 hybrids in a greenhouse setting from wild-collected seeds tied to vouchers allows for references to other wild-collected samples, bridging the gap between two hybridizing and introgressing taxa.