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 frame our research in a number of related areas, including: basic understanding of relationships among taxa, 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. 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 unanswered about their phylogenetic relationships, genome structure, and the physiological traits that have allowed them to persist and diversify. In particular, polyploidy and other reticulate processes (e.g., hybridization, introgression) are 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. Research on ferns and lycophytes in our lab focuses on several major areas of inquiry, including biogeographic patterns, diversification processes, mating systems, community assembly, genomics/transcriptomics, and physiological ecology, all of which we generally approach from the context of phylogeny.

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Our work, whether on ferns and lycophytes or other systems, depends on data collected via field and experimental studies and 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. There are many ongoing projects in the lab, including those listed below.

Flagellate Plants

This is a collaborative effort to build phylogenies for flagellate plants: gymnosperms, ferns, lycophytes, mosses, liverworts, and hornworts.

African ferns

Little is known about phylogenetic relationships or historical biogeography of African ferns and we are working to rectify this.

Community Phylogenetics

We are using phylogenetics and niche modeling to study community assembly of Florida ferns and south Florida’s endangered Pine Rocklands.

Dryopteris and Asplenium

We study phylogenetics, biogeography, and reticulate evolution of the Dryopteris and Asplenium, the woodferns and rockferns.

Fern genomics

Ferns are the only major lineage of land plant without a nuclear genome reference sequence; we are part of collaborative efforts to change this.

Fern mating systems

Ferns are capable of an extreme form of inbreeding, and we are interested in the implications for fern ecology and evolution.


The OneKP project has sequenced transcriptomes for more than 1,400 species of plants, from algae to angiosperms.


Goodeniaceae is a family of flowering plants that is diverse in Australia and related to the sunflowers.


Current members of the Sessa lab.


List of publications by lab members.


Courses taught regularly by Dr. Sessa.


The lab’s outreach and educational activities.

Lab News

Recent happenings in the Sessa lab.