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 a strong emphasis on the seed-free vascular plants: ferns and lycophytes. The primary question motivating much of our research is:
What ecological and evolutionary processes have generated, and maintain, fern and lycophyte diversity on earth?
Ferns are the second largest group of vascular land plants (ca. 10,000 species), and lycophytes (ca. 1,300 species) are sister to ferns+seed plants. Ferns and lycophytes have historically been underrepresented compared to other plant lineages in studies of phylogenetics, genomics, and physiological ecology, and as a result many questions remain about their phylogenetic relationships, genome structure, and physiological traits that have allowed them to persist and diversify. In particular, polyploidy and other reticulate processes (e.g., hybridization, introgression) are now recognized as critical phenomena that have shaped the evolutionary trajectories of many plant lineages, and ferns have the highest rates of polyploidy among vascular plants. Despite this, the specific effects of reticulate processes on patterns of relationships and biogeography, genome organization, and physiological ecology, are still largely unexplored in this lineage.
Our work focuses on six major focal areas: phylogenetics, physiological ecology, genomics/transcriptomics, biogeography, fern mating systems, and fern community assembly. We collect data via field and experimental studies and Sanger and next-generation sequencing, and integrate techniques from several disciplines, including computational and evolutionary genomics, phylogenetic systematics, physiological ecology, and traditional specimen-based botany. There are many ongoing projects in the lab, including those listed below.