Fern Phylogenetics

The phylogenetic relationships and evolutionary histories of various groups of ferns are a major area of interest in the Sessa lab. Two primary genera that we focus on are Dryopteris (the woodferns), and Asplenium (the rockferns). For Dryopteris, we are working towards constructing a worldwide phylogeny for all 400+ species that will serve as a basis for revising the global classification system for the genus. This is a collaboration with Libing Zhang (Missouri Botanical Garden), Aino Juslén, and Henry Väre (Finnish Museum of Natural History). We are also investigating the history of reticulate evolution in both Dryopteris and Asplenium, focusing on species complexes in North America, Europe, and Africa, in order to assess the relative frequency of recurrent polyploidization and its potential effects on genetic variation and implications for species concepts. Related studies on the North American species have investigated physiological traits and whether there is evidence that North American Dryopteris taxa are adapted specifically to the light environments in which they most commonly occur. In a Mediterranean complex of Asplenium, we are trying to determine whether there is evidence from chloroplast markers for asymmetric hybridization among members of the group. This project is a collaboration with José Maria Gabriel y Galan and his students (Universidad Complutense Madrid), and we are also working together on phylogenetics of Blechnaceae, including the genus Lomaridium and others.



  • Sessa EB. (2018) Evolution and Classification of Ferns and Lycophytes. Pages 179–200 in: Current Advances in Fern Research. H Fernández, Ed. Springer: Cham, Switzerland. Request PDF
  • PPG 1: The Pteridophyte Phylogeny Group*. (2016) A community-derived classification for extant lycophytes and ferns. Journal of Systematics and Evolution 54(6) 563-603.  PDF


  • Sessa EB, M Vicent, SM Chambers, and JM Gabriel y Galán. (2018) Evolution and reciprocal origins in Mediterranean ferns: The Asplenium obovatum and A. adiantum-nigrum complexes. Annals of the Missouri Botanical Garden. 103(2) 175–187. PDF


  • Vicent M, JM Gabriel y Galán, and EB Sessa. (2017) Phylogenetics and historical biogeography of Lomaridium (Blechnaceae, Polypodiopsida). Taxon 66(6): 1304–1316. PDF


  • Sessa EB, A Juslén, H Väre, and SM Chambers. (2017) Into Africa: Molecular phylogenetics and historical biogeography of sub-Saharan African woodferns (Dryopteris). American Journal of Botany. 104(3): 447–486. PDF
  • Sessa EB, L-B Zhang, H Väre, and A Juslén. (2015) What we do (and don’t) know about ferns: Dryopteris as a case study. Systematic Botany 40(2): 387–399. PDF
  • Sessa EB and TJ Givnish. (2014) Leaf form and photosynthetic physiology of Dryopteris species distributed along light gradients in eastern North AmericaFunctional Ecology 28(1): 108-123. PDF
  • Sessa EB, EA Zimmer, and TJ Givnish. (2012) Unraveling reticulate evolution in North American Dryopteris  (Dryopteridaceae). BMC Evolutionary Biology 12(1): 104. PDF
  • Sessa EB, EA Zimmer, and TJ Givnish. (2012) Reticulate evolution on a global scale: a nuclear phylogeny for New World Dryopteris (Dryopteridaceae)Molecular Phylogenetics & Evolution 64(3): 563-581. PDF
  • Zhang L-B, L Zhang, S-Y Dong, EB Sessa, X-F Gao, and A Ebihara. (2012) Molecular circumscription and major evolutionary lineages of the fern genus Dryopteris (Dryopteridaceae). BMC Evolutionary Bio 12(12): 180. PDF
  • Sessa EB, EA Zimmer, and TJ Givnish. (2012) Phylogeny, divergence times, and historical biogeography of New World Dryopteris (Dryopteridaceae). American Journal of Botany 99(4): 730-750. PDF