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Link to the Polystichum Homepage

David Barrington

Dr. David BarringtonProfessor of Plant Biology
Director of the Pringle Herbarium (UVM's plant systematics and conservation collection resource)

Ph. D. 1975, Harvard University

Research Area: Plant Systematics and Evolution

Email: David.Barrington@uvm.edu
Phone: 802-656-0431
Office: 310 Jeffords Hall

Courses Taught:

Biology of Ferns (PBIO 209) Tropical Plant Systematics (PBIO 241)
Systematics & Phylogeny, the summer version (PBIO 109) Botany Field Trip - Plant Diversity in Costa Rica, January of odd years (PBIO 232)
Exploring Biology (BCOR 12)  

Curriculum vitae (PDF)

Mailing Address:
Plant Biology Department
111 Jeffords Hall
63 Carrigan Drive
University of Vermont
Burlington, VT 05405 USA


The Barrington Lab at the University of Vermont is a community of scholars and students working together on an array of inquiries into the diversity and evolution of spore-dispersed plants, especially ferns and clubmosses. Our present group includes:

Michael Sundue, post-doctoral fellow specializing in Grammitid ferns. Funded by NSF with Tom Ranker for work on the systematics of Old World grammitid ferns, Michael also serves as assistant curator and librarian at the Pringle Herbarium.

Wes Testo, PhD candidate working on Huperzia

Brendan Lyons, undergraduate majoring in Plant Biology working on Polystichum

Heather Driscoll, guest researcher working on hybridization and apomixis in Thelypteris and Polystichum

Though we usually work on ferns (notably Polystichum, Phegopteris, Dryopteris, Matteuccia, and Polypodium) and Lycophyes (Huperzia), we have been known to work on flowering plants (including Carex and Lathyrus) as well. All of our projects include molecular genetic analysis of the plants: our data sets include an array of chloroplast DNA markers. A continuing theme in the lab is the understanding of hybridization and polyploidy in speciation histories. We have developed four "low-copy" nuclear markers to include in our studies, GapCp, PGIc, LEAFY, and ITS.

Among our nuclear markers PGIc is especially prominent. One of the long-term goals in our lab is the exploration of the whole PGI gene with the goal of an integrated understanding the evolution of introns and exons in this gene, ideally with reference to environmental variables such as temperature optima for gene function. Brendan has as the focus of his research the exploration of genetic variation in PGIc across Polystichum species with reference to their environmental preferences.

At the same time, we are deeply interested in the evolution of plant structures, so we have developed a number of tools for representing plant structural features and analyzing them phylogenetically. In all of this work, we find the geological context for our study to be of interest.

Undergraduate research has been a strong tradition in my lab. Recent graduates who completed projects in our lab include:

Morgan Moeglein, who worked on the hybrid between the two Vermont polypodiums using measurement of fluorescently stained nuclei

Dan Koenemann and Jacqueline Maisonpierre, who were central to our work on the fiddlehead fern (Matteuccia struthiopteris)

Kel Cook, who inherited the Polypodium project from Morgan, worked successfully to develop a combination of stomata length and spore regularity data to delimit the species and hybrids

Jacqueline used AFLPs to represent genetic diversity in Matteuccia (see Koenemann et al. below) In the course of her work we developed a healthy distrust of the data and attacks on solutions to data weaknesses.

Cathy Paris works closely with us in developing our research projects; she has her own website here.

Current Projects

For many years I have been interested in the fern genus Polystichum, which includes well-known ferns such as the sword fern of the American northwestern forests and Christmas fern, widely distributed in the eastern United States. The European holly fern Polystichum aculeatum is a well-known species, and the Eastern Asian Polystichum tsus-simense is commonly sold as a houseplant. Mere interest in a perversely difficult group originally attracted me to the genus, but as I have worked with the group, its appeal to me as a system for understanding problems in speciation, hybridization, and phylogeny has steadily grown. Much more detail on the genus Polystichum is available at the Polystichum Homepage, which I maintain.

There are four major research directions in my work on the genus Polystichum.

1. Circumscribing the phylogeny of Polystichum and its allied genera with molecular character sets

Polystichum tripteron in Japan

I remain most interested in the evolutionary history of Polystichum in the American tropics. My early work on the morpholoy and chromosome behavior of species and hybrids established a species concept and a sense of the morphological diversity in Latin America. Isozyme variation and meiotic chromosomal behavior proved to be powerful in testing hypotheses for hybridization and polyploidy (e.g. Barrington 1990), but little sense of the evolutionary history of divergence was to be gained from these datasets. About 1992 it became clear that further progress with Polystichum in tropical America would necessitate developing a basic phylogeny for the whole genus. Given the size and distribution of the genus (about 260 species worldwide, with endemic centers in China, Mexico, Africa, the austral regions of South America, New Zealand, and Australia, and minor regions elsewhere), this is an intimidating task. No consistent infrageneric classification based on a worldwide analysis exists, though there is an abundance of subgeneric taxa.

Working with then undergraduate Damon Little, now a curator at the New York Botanical Garden, I used a combination of molecular (rbcL) and morphological characters to develop a working phylogeny for Polystichum and its allies. This work (Little and Barrington, 2003) established a primitive idea of the relations and history of the genus. My work with master's candidate Heather Driscoll (now at Berkeley) on the origin of the three Hawaiian species of Polystichum (Driscoll and Barrington, 2007) was our next step in developing a world phylogeny (See this tree). This phylogeny reveals that species from the same geographic region are more likely to be related than are species with similar morphology. The most surprising and enlightening example of this pattern was discovering that the allegiance of the very similar P. lemmonii and P. mohrioides (sometimes treated as one species!) was to species from their own region (western North America and austral South America and the Antarctic Islands respectively) rather than to each other.

Polystichum bonseyi, Hawai'i

At this point, I was fortunate to be approached by two different groups of Chinese researchers working on the polystichums there. What ensued can only be called an Asian explosion, as we have since worked together to elaborate multisequence phylogenies rich in species from China, the world center of diversity for the genus (Lu et al., 2007; Li et al., 2008). Dr. Li Chun-xiang and I are now collaborating on building a phylogeny from a much-expanded dataset (working phylogeny based on four sequences for 130 species representing all endemic centers in the genus is available on the Polystichum homepage). We are also working on developing a species concept for Chinese Polystichum through analysis of hybrids, polyploids, and apomicts in the Polystichum tsus-simense group.

This array of work leads me to suggest that the significant clades in the genus are in general confined to endemic centers -- about a dozen of them - in regions already known for their diversity in other groups. W world diversity map based on our recent work is available on the Polystichum homepage. Three regions in Eastern Asia and the Andes emerge as the most diverse centers for Polystichum in the world.

2. Exploring pattern and process of divergence using molecular and biogeographic contexts in tropical America

bonapartii pinnae
Polystichum bonapartii pinnae, from Ecuador

The most important result of the world-level molecular analysis for me has been our demonstration that the New World tropical species we sampled constitute a monophyletic group. Taking advantage of this insight, Ph.D. candidate Monique McHenry is interpreting geographic and elevational distribution of a clade of species from the northern and central Andes that lack the true indusium typical of most polystichums. Monique was an invited speaker at the Botany 2010 symposium addressing the use of herbarium materials in modern fern systematics (abstract). We hope in this work to discover the isolating mechanisms that have operated in yielding the great diversity of species in the region (over 40 species in the continental neotropics, over 30 in the West Indies). We continue to be interested in morphological evolution - rapid changes in leaf dissection during recent evolution in the Andes are particularly striking, but we also have potential insights into the impact of exploring the tropical alpine on the morphology of these plants. We have been fortunate in our collaborators here - Klaus Mehltreter, Marcus Lehnert, Michael Kessler, Mike Sundue, and Jürgens Kluge have all sent substantial sets of plants. It has been our great fortune to host Brazilian Ph.D. candidate Joao Condack (Universidade Federal do Rio de Janeiro), who is working on the diversity of Brazilian Polystichum. Joao has made great progress in locating Polystichum populations in southeastern Brazil, and during his time with us in the summer and fall of 2010 he was able to make substantial progress towards understanding the phylogeny and historical biogeography of the Brazilian polystichums. In sum, there is a strong connection to the Andean lineage that Monique is studying, but there is a second lineage, including P. auritum, that evidence relations to the array of polystichums now found in southern Africa, southern South America, and Australasia.

We are happy to help anyone in Latin America with identification, to the best of our current ability.

The potential to use all these tools together to discover the patterns of ecological and geographic isolation that lead to the diversity in these montane regions is tantalizing; it inspires all we currently do with our work in the lab.

3. Understanding the edges between species as they are complicated by hybridization and polyploidy

Working in New England and tropical America, I have used a combination of isozyme markers, morphometric characters, and chromosome analysis to expand upon the classic works on hybridization and polyploidy on the genus contributed by Manton (1950) and Wagner (1963). It is clear that in the montane regions of the American tropics, just as in the north-temperate, Polystichum is involved in an array of reticulate (hybrid) interactions. My tropical work, which centers on the Talamanca range of Costa Rica and Panama, reveals that hybrids are common and that allopolyploidy, the origin of species through hybridization and doubling of chromosomes, is a contributor to species diversity (three of 12 Costa Rican species are polyploid). A spin-off of this work is my analysis of the composition of the fern flora above treeline in Costa Rica for a book on the páramos of that country (Barrington, 2005).

It has become clear from this work that a new assault on the role of polyploidy in the origin of species is relevant to discovering the general patterns of evolution in Polystichum. Consequently, over the past few years we have identified a set of nuclear sequences (five total, drawn from gapCp, PGIc, LEafy, and ITS) that we can analyze via cloning and direct sequencing to recover multiple genomes from polyploids and hybrids, with the goal of tracing their individual phylogenetic relationships. Expect a first publication introducing our work on this before too long. Details available to interested labs.

One of the undergraduate projects in the lab using these tools is likely to be the first to see the light of day (i.e. publication). Stacy Jorgensen, now a master's candidate in the lab, explored the origins of the three known tetraploids in Costa Rica, a country that has been at the center of our work on Polystichum since 1978. Stacy and I are wrapping up an expanded version of her undergraduate thesis with a close analysis of the constituent genomes of the three tetraploids using both direct sequencing and clone sequences of two of our sequences (gapCp and PGIc(exons 14-16).

Graduate student Stacy Jorgensen is using the tools we have recently developed for her master's project, which will focus on the origin of our only Vermont polyploid Polystichum, P. braunii. This species is circumpolar, and thanks to correspondents in Europe and Alaska, as well as our own National Geographic Society funded fieldwork in western China, we already have the material we need for exploration of its origins in a global context.

4. Allied nomenclatural and floristic work on Polystichum.

In the process of developing my interest in Polystichum I have of necessity sought to control the immense nomenclatural problems associated with naming species in the genus and providing floristic treatments. I maintain a virtually complete nomenclatural database for the genus, which I am happy to use as a basis for answering any questions colleagues have about names in the genus. A list of currently recognized species (to the best of my knowledge) with their basionyms and geographic distribution is included on the Polystichum homepage.


Matteuccia fiddleheads fiddleheads

Our work on the Quaternary Biogeography of New England (Paris and Barrington, 2007) has led us to open a new line of research, into explaining the historical origin of the distribution of genetic diversity in local ferns -- casting the problem in the context of a classic duality in population genetics. We are studying genetic variation in the fern commonly collected as a food (the fiddlehead fern, Matteuccia struthiopteris) with the idea of tracing its patterns of genetic diversity. Our work towards this goal is with nuclear gene introns and AFLPs. Undergraduates Dan Koenemann and Jacqueline Maisonpierre have pursued this interesting problem. This work is funded by CSREES funding through the Vermont Agricultural Experiment Station.

We have revealed, first of all, that this species is remarkably undifferentiated genetically - there is no cpDNA variation anywhere in the North American plants we have sampled. Our rapidly evolving nuclear intron PGIc(15-16) revealed minimal divergence, allowing us only to differentiate between Old World and New World plants.

AFLP analysis revealed substantial structure. Among northeastern North American populations, it appears that genetic diversity is greatest among plants from western Vermont, and progressively more depauperate north and east as far as the Gaspé Peninsula. This pattern is consistent with other work on northeast North American plants, leading us to postulate a Mississippi Valley refugium for the New World populations in the Pleistocene. Much more to do here, especially in developing nuclear-sequence witnesses to this history. Our current funding is focused on the exploration of our best-understood gene, PGIc, with the goal of characterizing evolutionarily significant variation across as much of the gene as possible, as has been done for oysters and butterflies.

Past Graduate Students and their Projects

Julie Dragon --- Carex systematics and biogeography

Heather Driscoll --- Origins of Hawaiian Polystichum

Stacy Jorgensen --- The Origin of Polystichum braunii

Monique McHenry --- Systematics and Evolution of exindusiate Andean Polystichum

Sonja Schmitz --- Lathyrus japonicus historical biogeography

Erin Sigel --- Monophyly or polyphyly: origins of Dryopteris campyloptera and dilatata

Recent, Favorite, and Forthcoming Publications

Note: linked publications are to PDFs

January 2013
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