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As a plant systematist, I am captivated by the migration and evolution of plant lineages into their current diversity and distributions, and the insights gained from such histories into the nature of species. Plant systematic and evolutionary biology has been built from centuries of taxonomic synthesis to name and categorize biodiversity via plant collections stored in herbarium institutions worldwide.
In our era of global change, it is essential to continue advancing the fundamental "boots on the ground" and "eyes in the herbarium" objectives of exploration and taxonomy with broader analyses of global ecological and evolutionary patterns. To fulfill this challenge, I have established an interdisciplinary botanical research program focused on enhancing our understanding of plant diversity through field, laboratory, and herbarium studies. These aims are currently applied across four main projects:
1) Taxonomy, biogeography, and diversification of the coca family (Erythroxylaceae)
Understanding why biodiversity is unevenly distributed across biomes and continents is a fundamental question in biology. My work has positioned the Erythroxylaceae family, a pantropical clade of about 300 species with over 75% of species (230/300 spp.) occurring in the American tropics, as a model clade for investigating these patterns.
The broad goal is to understand how the clade has moved across the globe in space and time as it diversified into about 300 modern species, and what ecological axes and key evolutionary innovations helped to define this evolutionary history. My thesis work showed that evolution between wet and dry forests has been frequent during diversification, framing several active investigations into the genetic underpinnings of these shifts.
This image is derived from a figure in White et al. (2019), wherein I published the first phylogeny (evolutionary history) of this plant group from DNA sequences, gaining insight into how this clade has diversified into different geographical and ecological regions. This work began with Hyb-Seq data and species continue to be added with whole genome resequencing. There are now over 230 species in the Erythroxylaceae phylogeny out of the approximately 300 species.
Constructing a genome for coca has been a central part of this research program, and thanks to collaborations with Iridian genomes, we sequenced, assembled, and published the first two coca genomes as well as genomes from 56 wild Erythroxylum species in 2022. I continue working to improve these assemblies and apply them in my evolutionary investigations.
2) Phylogeography, origins of domestication, and evolution of the coca crops (Erythroxylum spp.)
A fundamental revision of the domestication of coca was published in Systematic Biology. Using the Hyb-Seq method to sequence and analyze 424 genes, my colleagues and I studied the genetic diversity and relationships of the four varieties of coca and their two closest wild relatives, finding that Erythroxylum gracilipes (outlined in green) was the source plant of three independent domestication events that created the coca crops. This reveals that different ancient South Americans transformed the same wild resource (E. gracilipes) in parallel to create a primary commodity. It is clearly a useful plant!
I am in the process of analyzing whole genomes for hundreds of individuals in the 'coca clade' with careful geographic sampling. Over the next year these data will reveal a new and detailed picture of the history of the coca crops; establishing robust hypotheses on the dynamics and geographic and temporal origins of each domestication event, and the phylogeographic patterns shaping our modern diversity.
3) Floristics, biogeography, in situ and ex situ conservation in the Chocó cloud forests of western Ecuador
Since 2017 I have been studying the flora of the legendary Centinela Ridge in the Santo Domingo Province of Western Ecuador, the namesake of the Centinelan Extinction hypothesis. The story of Centinela was featured in several important conservation papers in the 1980's, culminating with Myers' (1988) framing of the Biodiversity Hotspot concept.
Our discovery in 2021 that the flora of Centinela has survived and still holds many botanical novelties has sparked an collaborative project with Juan Ernesto Guevara Andino of the Universidad de Las Américas and other academic institutions to systematically inventory the flora of Centinela and nearby Andean cloud forests to improve our knowledge of the biodiversity and biogeography of these extremely threatened ecosystems.
We have also teamed up with the conservation NGO Fundación Jocotoco and the Jardín Botánico Padre Julio Marrero to establish a reserve at Centinela and safeguard the most threatened of these species in their native habitats and through transplanting to botanic gardens. Read on at the ¡Viva Centinela! page and our dedicated website.
¡Que Viva Centinela!
4) Field and herbarium-based leaf reflectance spectroscopy for taxonomic classification and functional trait estimation.
The pressing demand for precise species identification and global biodiversity science is accelerating the use of innovative phenotyping tools. We are leveraging leaf reflectance spectroscopy to create high-throughput, integrated phenotypic spectral datasets. These spectra allow us to train machine-learning models capable of accurately identifying leaves to species or higher taxonomic levels and predicting leaf functional traits.
Spectral data serves as a valuable tool to evaluate the phenotypic cohesion of taxonomic hypotheses, positioning it as a crucial element in developing objective species delimitation methods.
As a test of the power of leaf spectra at the lower ranks of taxonomic classification, I worked in 2020 with a team in the interior of Alaska to first infer the population structure of ecotypes Dryas alaskensis and D. ajanensis using genomic methods, and then test to see if leaf spectral reflectance profiles could delimit the same structure. We successfully trained algorithms to classify leaves by species, hybrids, and mountaintop populations! Learn more in New Phytologist, and watch the Discovery Files episode.
My ongoing research on trait estimation, in collaboration with Jeannine Cavender-Bares, Charles Davis, and Dudu Meireles, focuses on proof-of-concept analyses of northeastern North American species, utilizing existing fresh and dry leaf trait models. This methodology is rapidly gaining traction, especially following the symposium I organized with Dudu Meireles and Thomas Couvreur at the International Botanical Congress in 2024. I am currently organizing the Herbarium Spectral Scanning Working Group with Jeannine and Dudu, with participation from 17 global herbaria.
Additional Projects
Additional Projects
Dryas ajanensis
Resolving a century of taxonomic confusion: Phylogeographic analysis of the global diversity and biogeography of Mountain Avens (Dryas, Rosaceae)
There is a big problem when studying the enigmatic, widespread Arctic dwarf shrub called Dryas (see above section): Dryas is a taxonomic mess with three valid naming systems describing 4-26 taxa. The clade is spread across the whole Arctic region and the plants frequently hybridize, producing a gradation of characteristic leaf forms. To fix this problem, I am currently working on a global phylogeny for Dryas to elucidate evolutionary lineages and species boundaries. In collaboration with members of the Natural History Museum at Oslo and the Polish Botanical Institute, we have sequenced 396 specimens representing all described taxa across their geographic ranges.
We are using phylogeny and species delimitation methods to establish a new and robust taxonomy for Dryas so that researchers can finally have a stable set of species names to work with. Beyond that, we are investigating the biogeographic patterns and drivers of diversification in this enigmatic and keystone clade.
Conservation genomics of the Endangered Pedicularis furbishae (Orobanchaceae).
Dubbed a "fugitive" species, Furbish's lousewort is constantly on the run to establish subpopulations in recently disturbed, north-facing riverbank habitats along the Wolastoq-St. John River in Maine and New Brunswick. This is classic microendemic was among the first eleven plant species to be listed on the U.S. Endangered Species Act (1978). Since 2020, there has been a drastic decline of individuals surviving in New Brunswick, and Natural Resources Canada (NRCan) is using population genomics to help save the species from extirpation and beyond.
With partners at the Field Museum, University of Maine, and Natural Resources Canada, we have generated the first Pedicularis fubishiae genome and RAD-sequenced over 100 individuals throughout the watershed to first understand if there are discrete genetic populations of Furbish's lousewort, and if so, assess if they have different levels of genetic diversity and inbreeding. Martin Williams of NR-Can is now taking our findings to guide seed collection and greenhouse propagation initiatives, and will be transplanting and enriching populations at new and old sites in New Brunswick to help save this species.
Look for our paper in early 2025!
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