Research

I’m interested in developing a broad understanding of the ecological and organismal factors which contribute to the creation and maintenance of plant biodiversity.  Much of my work has involved the application of population genetics in a phylogeographic, phylogenetic or ecological context to  identify lineages and explore the evolutionary forces maintaining this diversity.

Secondarily I am interested in traditional taxonomic studies focused on the circumscription and identification of taxa and using the available data to complete revisionary taxonomic treatments.  I am also interested in the curation and management of herbarium resources.

Below are descriptions of the projects I am currently working on.


Speciation of the genus Quercus in Mexico and the Southwestern US

The genus Quercus is well known for frequent hybridization among closely related species and recurrent hybridization is an important evolutionary process in the generation of species biodiversity. But how does hybridization and the process of ecological speciation work together to result in the diversity of species we see?  Using species exhibiting clear disjunctions and ecological specificity I am examining these patterns of speciation and resulting gene flow. Currently I am looking at two different groups.

Subsection Racemiflorae 

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Quercus tarahmara

This natural group of red oaks consists of four species (Q. conzattii Trel., Q. radiata Trel., Q. tarahumara Spellenb., J.R. Bacon, & Breedlove, and Q. urbanii Trel.) which are united by the characteristic of producing acorns on racemose inflorescences and occur in the western Sierra Madre and southern Cordillera of Mexico. There is an apparent segregation of the species based on edaphic factors and elevation with the more restricted species (Q. radiata, Q. tarahmara, Q. urbanii) being more or less specialists on highly sterile, often mineralized soils. This work was begun a number of years ago when I was a post-doctoral fellow at the Centro de Investigaciones en Ecosistemas (CIEco) of the Universidad Nacional Autónoma de México (UNAM) in Morelia, Michoacán (now Instituto de Investigaciones en Ecosistemas y Sustentabilidad (IIES)). The research covering 49 populations shows a pattern of extensive gene sharing but also a pattern of species segregation based on ecological speciation, driven principally by edaphic factors.

Poster Presentation presented at the IVIII Botanical Congress, Melbourne Australia: Genetic Structure and Speciation in a Lineage of Mexican Red Oaks: A Phylogeographic Study of Quercus Section Lobatae Subsection Racemiflorae.

Quercus havardii

This species of white oak shows a disjunct distribution between the Colorado Plateau and sand plains of eastern New Mexico, Western Texas and Oklahoma.  While viewed as the same species this circumscription has been questioned and the evolutionary history is little known. To investigate this I am working on a project spearheaded by Sean Hoban at the Morton Arboretum to investigate the ecological, morphological, and genetic patterns seen across the complete species range.

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Sean with Q. havardii – Cedar Mesa, Utah


Systematics of Amaranthaceae

Evolution of the Endemic Hawaiian Arborescent Amaranthaceae

Together with my collaborator J. Christopher Havran at Campbell University we are investigating the phylogeny and origin of these unique genera in the Hawaiian Islands. Our studies are initially focusing on the development of a molecular phylogeny for the family to understand the dynamics of species relatedness and origin in the Pacific Basin. Our work to date has uncovered a close relationship between the widespread genus Achyranthes and Nototrichium, a potential intergeneric hybridization between Charpentiera and Achyranthes prior to long-distance dispersal, and a number of instances of paraphyly in the evolution of these groups. Our future work seeks to investigate at a more in-depth scale the patterns of evolution and corresponding classification of these species in the islands.

Poster Presentation presented at Botany 2014: “Paraphyly, hybridization, and multiple introductions in the origin and evolution of the endemic Amaranthaceae of the Hawaiian Islands (genera Achyranthes, Charpentiera and Nototrichium)

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Achyranthes splendens (Photo by Chris Havran)

Systematics of the genus Froelichia

The genus Froelichia is a group of 16 species of small herbs and shrubs native to a variety of habitats in the Western Hemisphere. During my masters and Ph.D. I worked extensively with this group on topics ranging from basic taxonomy to biogeography, population ecology, and phylogenetic reconstructions.

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Froelichia arizonica – Chihuahua, Mexico

After about a 10 year hiatus from work with the genus I am  getting back to it with an in-depth study of the genus in the Galapagos Islands.  Five taxa are endemic to the islands and during the first six months of 2017 I will be using a Fulbright Fellowship to work with collaborators at the Universidad San Francisco de Quito and the Charles Darwin Research Station on the completion of a revision and phylogeographical analysis of the Galapagos endemics.

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Froelichia procera – Paraguay

Phylogeny of the genus Gomphrena in North America

Gomphrena is a genus of approximately 100 species with a center of diversity in South America.  In North America there are between 8-15 species with the highest diversity expressed in parts of central Mexico and the southwestern United States.  The group has been little studied and current species circumscription may be over-simplifying the actual diversity.

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Gomphrena decumbens – Michoacan, Mexico

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Gomphrena pilosa – Michoacan, Mexico


Historical phylogeography of mesic forest species of the greater southwestern United States

Phylogeography of the genus Ostrya (Betulaceae)

Ostrya is a small genus of understory tree in North America and Asia commonly known as hop-hornbean. In North America the genus ranges from southern Canada to Honduras with most of the morphological variation found in the southwest US and mountains of Mexico. The genus shows a relictual distribution pattern with occurrences across the southwest being in small isolated locations near mountain tops and isolated valleys and in Mexico as a cloud forest endemic.

Results of morphological investigation of species circumscription of Ostrya in the American Southwest (Collaborative Student/Faculty Research): “A taxonomic reevaluation of the genus Ostrya (Betulaceae) in the Southwestern United States based on leaf morphology

Results of preliminary analysis of molecular phylogeography across the SW United States and Mexico “A preliminary analysis of phylogeography and species diversification of Ostrya (Betulaceae) in the southwestern US and Mexico

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Ostrya knowltonii

Phylogeography of the western Sugar Maple – Acer grandidentatum

Acer grandidentatum exhibits a disjunct distribution in isolated locations across the soutwest with an extension north to southern Idaho. Much like Ostrya the distribution is likely relictual from a wider historical distribution and is a good model system for investigating mesic forest element phylogeography across the greater southwest.  I am in the early stages of this research focusing principally on broad population sampling.

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Acer grandidentatum – Abajo Mts., Utah