Research in the Sessa lab focuses broadly on plant systematics and understanding the evolutionary and ecological processes that shape plant diversity. Lab members work on a number of projects around this central theme, with phylogenetics as the unifying conceptual framework. Phylogenies inform our research in a number of related areas, including understanding basic relationships among taxa, patterns of reticulate evolution, diversification rates and biogeographic history of organisms, community phylogenetics, and trait evolution using comparative methods. Organismally, we have a strong focus on the seed-free vascular plants: ferns and lycophytes (traditionally collectively called pteridophytes). Our work, whether on ferns, lycophytes, or other systems, uses data collected in field and experimental studies and generated via Sanger and next-generation sequencing. We integrate techniques from several disciplines, including computational and evolutionary genomics, phylogenetic systematics, physiological ecology, and traditional specimen-based botany.

Learn more about ferns and lycophytes by clicking below, or visit the Research page to learn about current projects in our lab.

More about ferns and lycophytes…

Ferns are the second largest group of vascular land plants (ca. 10,000 species), and lycophytes (ca. 1,300 species) are sister to the ferns plus the seed plants (the euphyllophytes). Ferns and lycophytes are therefore not a clade, but have historically been associated with one another as the spore-bearing vascular plants, or pteridophytes. These lineages have tended to receive less attention than the mega-diverse seed plants in studies of phylogenetics, genomics, and physiological ecology, and as a result many questions remain unanswered about their phylogenetic relationships, genome structure, and the physiological traits that have allowed them to persist and diversify.

Ferns are the major focus of work in our lab, and they are fascinating for many reasons, including their huge genomes and high chromosome numbers, interesting physiological ecology and biogeographic patterns, and mating behavior that allows for extreme selfing. Polyploidy and other reticulate processes (e.g., hybridization, introgression) are also recognized as critical phenomena that have shaped the evolutionary trajectories of many plant lineages, and ferns have some of the highest rates of polyploidy among vascular plants.