March 29, 2022 Monthly Program of the Maryland Native Plant Society www.mdflora.org

The Orchidaceae is one of the most species-rich plant families, representing nearly 10% of flowering plant species. Evolution of specialized pollination syndromes and adaptation to a variety of habitats has been connected to large radiation events in Orchidaceae, but orchids’ symbiotic relationship with specific fungi may also play a role in diversification in the family. Orchids depend on associations with particular mycorrhizal fungi for nutrition throughout their life cycle. Orchid distribution is influenced by the availability of compatible mycorrhizal fungi, particularly when orchids require specific fungi. Specificity of orchids for mycorrhizal fungi remains controversial, with no clear patterns determining the range of fungi compatible with different orchid species. Different fungi may grow in distinct environments, so associations with fungi may also influence whether orchid species co-occur or are environmentally segregated. Where closely related orchids co-occur, they may form hybrids.

Hybridization is a mechanism of speciation for many plants, especially orchids. Orchid hybridization is not limited to the hybrids produced by orchid growers. When closely related species grow in the same habitats, natural hybrids occasionally occur. If hybrids use different fungi than their parent species, then they may colonize places where the parent species cannot grow and possibly evolve into new species.

We used a combination of floral morphology and DNA sequencing to identify hybrids and studied whether hybridization and differential specialization on specific fungi contribute to speciation processes in orchids, using the genus Platanthera, the fringed orchids, as a model system. Platanthera is the largest orchid genus in North America and contains several complexes with closely related species that can be challenging to tell apart morphologically. We focused on two species complexes that include both recent hybrids and species of proposed hybrid origin. We also considered additional species within and outside of these hybrid complexes. We used a combination of fungal cultivation, DNA sequencing, cross-pollination, and seed germination experiments to test the hypotheses that 1) the identity of fungal associates reflects plant phylogenetic relatedness, and 2) specificity in fungal associations differs among orchid species, as well as between hybrids and parent species. The results suggest that fungal associations may affect orchid speciation and co-existence. We discuss how this information has implications for defining species, setting conservation priorities, and conserving orchids.

Speaker. Melissa McCormick is an Ecologist at the Smithsonian Environmental Research Center, where she has studied orchids and other plants since 1999. She received a BS in Biology from Trinity University in San Antonio, Texas and a PhD in Ecology, Evolutionary Biology and Behavior from Michigan State University. She uses a combination of field and DNA-based techniques to study plant-fungus interactions, plant conservation, and plant invasions. Her main research focus is on orchid associations with mycorrhizal fungi and how they affect orchid rarity and distribution. She is also one of the founding members of the North American Orchid Conservation Center (NAOCC), which is a pioneering initiative to link botanic gardens, land managers, and researchers to conserve all the native orchids of North America. She has published over 50 papers, 25 of which have focused on understanding native orchids and their mycorrhizal fungi and how they are affected by land use history, drought, and non-native earthworms.

Speaker. Ida Hartvig has been a Carlsberg Postdoctoral Fellow at the Smithsonian Environmental Research Center since 2019, where she is exploring how fungi contribute to speciation and diversification in the orchid genus Platanthera. She considers herself a botanist as well as a molecular ecologist. She has a MSc in Plant Ecology and Evolution and a PhD in Conservation Genetics, both from University of Copenhagen, Denmark. Her research is motivated by a deep fascination with the complexity of nature and a desire to contribute to its conservation. Prior to immersing herself in the complex interactions between orchids and fungi, she worked with evolution of plant mating systems at the Galapagos Islands, conservation and landscape genetics of timber trees in Indochina, as well as application of eDNA and NGS barcoding methods in biodiversity monitoring and nature management in Denmark. She finds field trips and studying plant species in their natural habitats to be by far the best part of her work, and she has really cherished being able to visit awesome botanical localities in Maryland and adjacent states for her current project.

Recorded March 29, 2022

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