From Plant Press, Vol. 18, No. 3, July 2015.
By Gary A. Krupnick
Fern and lycophyte biology was the focus of the 13th Smithsonian Botanical Symposium, held 1–4 June 2015 at the National Museum of Natural History (NMNH) and United States Botanic Garden (USBG) in Washington, DC. Also marking the 12th Symposium of the International Organization of Plant Biosystematists, and titled, “Next Generation Pteridology: An International Conference on Lycophyte & Fern Research,” the meeting featured a plenary session on 1 June, plus three additional days of focused scientific talks, workshops, a poster session, a reception, a dinner, and a field trip. The conference brought together the world's pteridologists to celebrate the progress of fern and lycophyte biology to date and to forecast developments still on the horizon.
The Symposium began with opening remarks by Warren Wagner (Chair of Botany, NMNH), Kirk Johnson (Sant Director, NMNH), and Ari Novy (Executive Director, USBG). Eric Schuettpelz (Curator of Ferns, NMNH) served as convener. Noting that the last international conference on lycophyte and fern research took place 11 years ago at the Royal Botanic Garden Edinburgh, Schuettpelz expressed excitement as this year’s conference of 97 talks and 30 posters, including the 10 invited plenary speakers, was to focus on discussing new and revitalized methods for pteridological research.
After the opening remarks, Laurence Dorr (Curator and Cuatrecasas Committee Chair, NMNH) presented the 13th José Cuatrecasas Medal in Tropical Botany to Paulo Günter Windisch (see related story on page 12 of the newsletter). This prestigious award is presented annually to a scholar who has contributed significantly to advancing the field of tropical botany. Windisch, a retired professor from the Universidade Federal do Rio Grande do Sul, was commended for his extensive contributions to the systematics, biogeography, and evolution of neotropical pteridophytes. In his acceptance speech, Windisch expressed his appreciation and gratitude to the Smithsonian Institution and the selection committee. He said that receiving the medal rekindles his inner spirit, and remarked that “translating nature into science is an art.”
The first day of the Symposium included a plenary session that was open to the general public. With 10 invited talks, the audience was treated to an overview of fern and lycophyte evolution, genomics, physiology, ecology, horticulture, and conservation. The opening keynote speaker was Robbin C. Moran from the New York Botanical Garden, and his talk, “An Overview of Ferns and Lycophytes,” provided an exciting introduction into the world of pteridology. Starting with the life cycle of pteridophytes, Moran discussed the unique, independently living sporophyte and gametophyte generations of this plant group.
Moran also spoke about the differences between pteridophytes and seed plants in aspects of biogeography (ferns comprise a higher percentage of the total vascular flora on islands compared to continents), hybridization and polyploidy (ferns have higher rates), and anatomy (some ferns have tree-like growth using root mantle or have internal reinforcement by sclerenchyma instead of lateral meristem). Moran also provided a historical overview of pteridophytes in the Silurian to Early Devonian (at which time leaves originated); in the Carboniferous (pteridophyte swamps from that time were the precursor of today’s fossil fuel); at the Cretaceous-Tertiary Boundary (a spike in fern diversity can be seen soon after the asteroid impact); and in the Early Tertiary (warm weather produced thick carpets of Azolla in the Arctic Ocean leading to a sharp reduction in atomospheric CO2 reducing the greenhouse effect and lowering the Earth’s temperature). Moran concluded his talk with a discussion of iridescence in ferns, the diversity of sporangia, and the explosive sporangial dehiscence of the clubmoss Lycopodium clavatum. He explained how the spores of this plant, which are highly flammable because of their high fat content, were used as a “flash powder” in early magic acts, and he gave with a quick demonstration by lighting the spores on fire and taking everybody in the audience by surprise.
Patricia G. Gensel from the University of North Carolina at Chapel Hill gave a talk entitled “Silurian-Devonian Fossil Plants Provide Some Insights into the Evolutionary History of Ferns and Lycophytes.” Gensel began her talk by presenting the fossil candidates for the origin of pteridophytes. The earliest occurrence of trilete spores is found in the Mid-Late Ordovician (450-470 million years ago). These spores are produced by a very few living bryophytes but mostly seed-free vascular plants. The Silurian-Devonian (425-370 million years ago) fossil record shows evidence of the first occurrences of major plant structures: leaves, tracheids, and rooting structures. Several waves of vascular plant diversification occurred during the late Early Devonian: diverse zosterophyllophytes, leaves of early lycophytes, early barinophyte-like plants, and the diversification of basal euphyllophytes.
Gensel explained that the fossil evidence of plants bearing strobili provides confirmation that heterospory arose in lycopsids by the Middle Devonian. Other major events seen in fossils include a clear rooting structure in zosterophylls, leaves in early lycopsids starting in the Silurian, and upright lycopods (roots at one end and branches at the other end) as seen in Longostachys from the Middle Devonian. Gensel also discussed branching patterns in the fossil record and how architecture can be used to distinguish among taxa.
Paul G. Wolf from Utah State University spoke on “Fern Genomics: Progress and Prospects.” Wolf explained that since ferns are the sister group to seed plants, they can play an important role in comparative genomics. He noted that the mechanisms of gene and genome duplication are well studied, but processes that occur after genome duplication are not so well understood. He said that it remains unknown why homosporous ferns have so many chromosomes—flowering plants have an average base chromosome number of approximately 16 chromosomes whereas homosporous ferns have an average base chromosome number of approximately 57 chromosomes.
One hypothesis to explain the high chromosome numbers is that homosporous ferns undergo cycles of polyploidy and gene silencing more often than seed plants, but current research reveals that ferns are no more polyploid than seed plants, suggesting that ferns have different genome dynamics. When looking at repetitive DNA of ferns compared to seed plants, a higher proportion of simple repeats can be found in ferns. Wolf concluded his talk by appealing to the research community to complete the first genome sequence of a fern, suggesting two candidates for this endeavor—Azolla, an economically valuable group with a small genome, or Ceratopteris, a model experimental system with a large genome.
Alejandra Vasco from the Universidad Nacional Autónoma de México spoke on “Evolution and Development in Lycophytes and Ferns.” Lycophytes and ferns occupy key phylogenetic positions within land plants and thus provide a fascinating comparison (to seed plants) for evolutionary developmental studies. Vasco highlighted some innovations in the ancestral vascular plant lineage: naked and dichotomously branched axes, tracheids, terminal sporangia, and homospory. Some lineages of lycophytes and ferns contain other morphological novelties, such as ligules and the rhizophores in lycophytes and the abaxial position of the sporangia in leptosporangiate ferns. Vasco also spoke about the origin of leaves in vascular plants and how many times leaves have evolved. By studying morphology and the fossil record, she showed that the two main types of leaves, microphylls and megaphylls, have different origins. Paleobotanists have hypothesized that megaphylls in ferns and seed plants may be homologous (as lateral branches), but that the processes of flattening into one plane (planation) and the formation of a lamina (webbing) may have developed independently in two lineages. Experimental analyses of fern leaf development show that fern leaf primordia, like those of seed plants, arose from one or a group of cells on the flank of the shoot apical meristem in a distinct phyllotaxy.
Vasco continued by discussing the evidence from systematics and molecular biology of leaf evolution. She argued that dated phylogenies suggest that fern leaves evolved multiple times. Molecular genetics has identified some genes that play key roles in the processes that define a leaf. Various modern techniques such as transgenic tools, gene expression tools, and expression analyses are filling in gaps. She summarized some current findings: ferns and seed plants co-opted the same developmental mechanism for leaf development (deep homology), and the sporangial developmental program was co-opted independently for the development of leaves.
After lunch, Tony Avent from Plant Delights Nursery at Juniper Level Botanic Garden in North Carolina discussed fern horticulture in his talk “Exploration to Exploitation—the Road from Discovery to Market.” Avent presented a slideshow of fern species from the wild and in cultivation, which covered his experiences from more than 80 expeditions. The goals of these trips included finding unusual species and varieties, bringing back viable spores, and ultimately bringing the taxa into cultivation. His slideshow included images of ferns from Argentina, Bosnia, China, Crete, Croatia, Korea, Mexico, Slovenia, South Africa, Taiwan, and the United States.
In his quest, Avent prefers to find hardy individuals—those growing at high elevation, in deserts, or in the deep shade and standing water of swamps. Sometimes he will find a desired species but is unable to collect spores. Such was the case for Dipteris conjugata from Taiwan, what he calls “the coolest fern in the world.” In Crete he searched for a heat tolerant species and found Dryopteris pallida, “an elegant fern that can have a wonderful place in people’s gardens.” During his presentation, Avent received some help from the audience—after noting some difficulty identifying a puzzling species from Taiwan, an attending pteridologist shouted out “Plagiogyria”! Avent concluded his talk by saying that the fern cultivation potential in modern times is incredible and that we have entered a new Victorian era for ferns.
Hanna Tuomisto from the University of Turku, Finland presented “How Ferns Help to Unravel the Mysteries of Amazonian Biodiversity.” Tuomisto’s research focuses on species diversity patterns in the state of Amazonas in Brazil, an area under-collected compared to other tropical areas like Ecuador and Costa Rica. High in species richness for hummingbirds and beetles, a 1-hectare plot of forest in Amazonas may have 30 fern species and over 1,000 species of vascular plants. Her fieldwork has shown that geological formations are highly relevant for the ecology of ferns.
In testing the predictability of species composition patterns and environmental gradients in Amazonia, Tuomisto carefully studied the distribution patterns of several fern species: Lindsaea lancea, L. phassa, Danaea nigrescens, and D. cartilaginea. She found that soil cation concentration marks a clear separation in the fern flora on different sides of an Amazonian river. Estimating soil properties from fern distribution data can help explain why hunters bring back different amounts of meat from different parts of the rain forest. Extrapolating for the whole area can assist in estimating prey abundance for hunters. Tuomisto explained that species richness shows positive trends with environmental variables such as altitude, annual rainfall, and soil cation concentration.
Masamitsu Wada from Kyushu University and Tokyo Metropolitan University, Japan discussed “Photomorphogenesis of Adiantum capillus-veneris Gametophytes.” Wada began his talk by explaining that Adiantum gametophyte cells provide a model system for his studies because cell division is controlled by light. By applying various light treatments, Wada is capable of studying phototropic responses in cell biology. Wada presented his experiments on the timing of cell division and the movement of chloroplasts. Since the timing of cell division is light dependent, Wada demonstrated that blue light induces very fast division by shortening the G1 phase of cell division while red light slows it down.
Wada shared videos of chloroplast movement under different light conditions. If a plant receives light levels higher than those required for photosynthesis, a protective mechanism includes moving chloroplasts from the cell surface to the sides of the cell to reduce photodamage. This chloroplast avoidance movement has been found in algae, mosses, ferns, and many seed plants. Wada obtained Arabidopsis cell mutants deficient in this movement to understand the molecular mechanism behind the movement and found that actin filaments are predominantly utilized for chloroplast movement.
Marian M. Chau from the University of Hawaii at Manoa spoke on fern conservation in her talk, “From Endangered to Invasive: the Role of Fern Ecology in Conservation of Hawaiian Ecosystems.” For the first half of her talk, Chau discussed the experimental ecology of the endangered ‘ihi‘ihi fern, Marsilea villosa. She conducted vegetation surveys and measured soil characteristics, canopy cover, and flooding levels to determine the best growing conditions and to provide management recommendations for this narrowly endemic species. Based on her results, she recommends that restoration projects occur in areas with consistent flooding and with native tree species, and that non-native grasses should be controlled.
The second half of Chau’s talk focused on the effects that an invasive Australian tree fern has on Hawaiian soil and nutrient dynamics. Hawaii has four endemic Cibotium tree fern species, called hapu‘u, which act as keystone species by serving as hosts for epiphytes and sequestering more nitrogen and phosphorous than most other native vascular species. One of the worst invaders in Haleakala National Park is the Australian tree fern, Sphaeropteris cooperi, which is displacing Cibotium with its faster growth rate, higher photosynthetic rate, faster leaf turnover, and higher drought-tolerance. Chau studied how leaf litter of the two taxa affected native angiosperm growth. In an experimental study, she found that invasive leaf litter increased the growth of Carex and Hibiscus but not the slow-growing, dominant canopy tree Metrosideros. She concluded that even though the invasive tree fern’s altered nutrient cycling appears to have a positive effect on plant growth, the long-lasting effects may lead to an altered forest structure if it favors fast-growing native species over slow-growing species. She stressed that understanding fern ecology—both native and invasive—is critical to informed conservation practice.
James E. Watkins Jr. from Colgate University, and the current president of the American Fern Society, presented the talk, “Ecology and Ecophysiology of the Fern Life Cycle: Making the Best of a Double Life.” Watkins began his presentation with a look at the functional differences between gametophytes and sporophytes: gametophytes are relatively simple, with no vascular tissue or stomata, whereas sporophytes are more complex. Thus the two unique ecologies provide an interesting study system where the selective pressures acting on gametophytes are very different from those on the sporophytes.
Watkins studies fern epiphytism, a trait that has evolved multiple times in the ferns, and he explained how epiphytic ferns function relative to terrestrial species. He spoke about the remarkable variation in gametophyte morphology and explained that epiphytic gametophytes can be longer-lived, have a higher desiccation-tolerance, and are more capable of intragametophytic selfing than their terrestrial counterparts. He also spoke about sporophyte water relations in which epiphytes have smaller tracheid (conduit) diameters and are thus less likely to dry out. Watkins then presented two strategies in fern ecophysiology, in which terrestrial species are fast growing with simple morphology, and epiphytes are slow-growing with more complex morphology. He concluded that our understanding of fern physiology will provide informative knowledge as ferns respond to climate change and allow for predictive models in the management of endangered fern species.
The closing keynote presentation was by Kathleen M. Pryer from Duke University who presented “Communicating Science in Social Settings…Yes, It Matters.” Speaking on the powers of social media for science, Pryer began her talk by taking a selfie of herself with the audience and immediately posting it on Twitter. She argued that a current anti-science rhetoric is on the rise and that disbelief of evolution is too common in the US. She praised the advances in fern science—from understandings of the fossil record to technological breakthroughs in DNA sequencing. Yet fern biology has fierce competition when it comes to funding, especially when ferns are considered “lower plants.” Thinking of seed-free plants as “lower” is an old way of thinking. This has hampered her ability to fund her research on Azolla, a group of ferns with “massive green potential.” Bucking tradition, she crowdfunded an Azolla genome sequencing project. Crowdfunding not only raised enough seed money for the exploratory research, but also allowed the public to participate, support, and witness advancements in science.
Pryer also spoke about the public response when her research team named a new genus of ferns Gaga. The name honors the pop music star Lady Gaga, and was chosen because many fern gametophytes have a striking resemblance to one of Gaga’s famous costumes, they have a somewhat fluid definition of gender, they bear a distinct DNA sequence synapomorphy spelling GAGA, and the sporophytic fiddleheads look like her fans’ “claw greeting.” Not intended as a publicity stunt, Pryer said that the result of the naming episode allowed her to connect with a part of society she normally does not encounter. She enjoys making science connections with individuals who do not normally visit natural history museums or watch nature programs. She stated, “When scientists communicate effectively, science thrives.” She urges the scientific community to share their passion and to make science more accessible to a variety of communities.
Monday concluded with an evening poster session at the Conservatory of the United States Botanic Garden. An international group of 30 presenters displayed their posters and spoke about their research on ferns and lycophytes ranging in topics from taxonomy and phylogeny to biogeography and physiology.
The next three days featured five colloquia and four contributed presentation sessions. The colloquia were titled (1) Biogeographic patterns and processes of speciation and hybridization in spore-bearing plants; (2) Future challenges of fern and lycophyte ecology: a call for conservation and collaboration in the next generation; (3) Genomics and transcriptomics of ferns and lycophytes; (4) Evolution and development in ferns and lycophytes: case studies and perspectives; and (5) The integration of ecological and phylogenetic approaches in pteridology.
Thursday night featured a reception and symposium dinner in the Rotunda of NMNH. On Friday, three concurrent workshops were presented: (1) An introduction to next-generation sequencing and bioinformatics; (2) Digital species identification tools; and (3) Field ecology of ferns: a call for new standard methods and opportunities for collaboration among pteridologists. The final event of the conference was a field trip to Great Falls Park and Scott's Run Nature Preserve, where guests were treated to seeing native ferns growing in the DC region. Participants saw 22 fern species, a highlight among which was Homalosorus pycnocarpus (the glade fern), the only member of a monotypic genus and one of only two genera belonging to the otherwise Old World family, Diplaziopsidaceae.
Next year’s 14th Smithsonian Botanical Symposium will take place on Friday, May 20, 2016, with a theme still to be determined. Be sure to check the symposium website at <https://botany.si.edu/sbs> for updates.