The evolutionary history of polyploid fern lineages is often reticulate. Repeated hybridization and asexual lineages complicate phylogenetic reconstruction. In members of the holly fern genus native to China, Polystichum sect. Xiphopolystichum, genome inheritance looked liked this:
Even when the molecules paint a clear picture, morphology may not. Species of hybrid origins that share progenitors might appear very morphologically similar. It’s important to use a quantitative approach to distinguish them. Here’s what Xiphopolystichum looks like in terms of level of dissection.
Patel N, Li C, Zhang L, Barrington D. 2018. Biodiversity and apomixis: insights from the East Asian holly ferns in Polystichum sect. Xiphopolystichum. Molecular Phylogenetics and Evolution. 127: 345-355.
Patel N, Fawcett S, Gilman A. 2019. Phegopteris excelsior (Thelypteridaceae): A New Species of North American Tetraploid Beech Fern. Novon: A Journal for Botanical Nomenclature. 27 (4), 211-218
Along the way in studying these ferns, we used a few different approaches for assessing ploidy and sexual system. Spore size can inform ploidy, and spore number per sporangium can inform sexual system.
Barrington DS, Patel N, Southgate MW.2020. Inferring the impacts of evolutionary history and ecological constraints on spore size and shape in the ferns. Applications in Plant Sciences 8 (4).
Spores are incredibly diverse in form. What else could we learn from them? The ornamentation of fern spores, made of sporopollenin, is very varied and often species specific. Does this aspect of morphology have taxonomic implications? We explored this in the fern family Thelypteridaceae. This was a great opportunity to incorporate natural history collections into our research. We sampled spores from exclusively herbarium specimens, and imaged them using Scanning Electron Microscopy (SEM).
Indeed the shape of perine macrostructure is phylogenetically informative! SEM is a costly and involved process, but luckily many SEM spore images are already published. Revisiting these data can help refine taxonomy across ferns.
Patel N, Fawcett S, Sundue M, Budke J. 2019. Evolution of Perine Morphology in the Thelypteridaceae. International Journal of Plant Science 180 (9), 1016 – 1035.
What do we know about ecology and polyploidy? It’s been suggested that polyploids have a wider ecological tolerance than diploids. Hybrids in general seem to be intermediate to their progenitors both morphologically and ecologically. Is that true for a polyploid hybrid? The Adiantum pedatum complex in New England is a great system to explore this. It includes an allotetraploid and its progenitors. We found evidence for both niche intermediacy and transgression. My student Morgan was a whiz at fieldwork, and it doesn’t hurt that maidenhair ferns are simply beautiful!
Southgate M, Patel N, Barrington, D. 2019. Ecological outcome of allopolyploidy in Adiantum (Pteridaceae): Niche intermediacy and expansion into novel habitats. Rhodora, 121(986), 108-135.
We reconstructed evolutionary history in polyploid ferns, but it’s hard to know if polyploids form and are immediately reproductively isolated from their progenitors. Mosses offer an opportunity to experimentally test for reproductive isolation. We can artificially induce polyploidy in moss through apospory, and then perform reproductive crosses. We’re developing Physcomitrium pyriforme as a model system for this.