graduate students

Dylan Cohen

Doctoral Candidate


I am from Pittsburgh, Pennsylvania. I have two Bachelors of Science degrees (Communications Media: Indiana University of Pennsylvania, 2008; Environmental Studies: California University of Pennsylvania, 2015). I have always been curious about the natural world and attracted to the morphologically ‘bizarre’. Botany and mycology courses fed this addiction and undergraduate research experiences set me on a path towards my PhD.

I am in my fifth year at the RSA and have completed several seasons of field work in Argentina, Chile, and the Mojave Desert. Field and herbarium collections have been used to generate Rad-Sequencing data. Working with this data set has granted the opportunity to expand my bioinformatic skills. I plan on defending my dissertation in December 2020 and look forward to continuing my research career by obtaining a postdoc, faculty position, or research position involving collections.


My dissertation research involves several genera from Loasaceae (rock nettle) family and is broadly focused on biogeography, conservation, evolution, systematics, and taxonomy.

My first chapter details the evolutionary history for a clade of Mentzelia section Bartonia from the Mojave Desert. Section Bartonia is of recent radiation and species boundaries are obscured by similar morphologies. Several species are of conservation concern, and therefore delimiting boundaries is crucial for proper management. Next generation sequencing and morphological data are being utilized to establish species boundaries, to inform land managers and to understand the diversity of this group

The remaining chapters of my thesis address Loasa sensu lato from Argentina and Chile. Loasa is recognized for its striking floral morphology, composed of cup shaped petals, of which bundles of stamens are located immediately after antithesis. Petals and stamen are alternated by nectar scales and inner staminodes(sterile stamen). Colorful patterns and nectar rewards attract pollinators, and their activity can trigger stamen movement towards the center of the flower. This genus has recently been segregated into several genera based on morphology and chloroplast loci. The chloroplast genome is maternally inherited, and slower to evolve than the nuclear genome. I am using Rad-Seq to construct a nuclear phylogeny for Loasa s.l in order to test the present day classification and to investigate biogeographic patterns of Loasa within the southern cone region. The southern cone region is intermixed with diverse landscapes accompanied by extreme climates; the arid Atacama Desert, Meditterrean Chile, temperate rainforest, Patagonia steppe, and montane environments of the southern Andes. These features combined with the Pacific Ocean isolate Chile thus creating a continental “island.” Loasa s.l. is found throughout Chile, in all types of environments. Understanding biogeographic patterns and processes will help to unravel the complex evolutionary history of this charismatic group.

Additional Information

Follow my adventures via Twitter: @DylanHCohen


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