Today on Mushroom Hour we are joined by illustrious lichen expert Matthew Nelsen PhD. Matthew is a Research Scientist at the Field Museum of Natural History in Chicago. Matt's research began in botany, ecology and environmental science and has more recently gravitated towards: (i) the evolution of symbiotic associations; and (ii) the evolution of eukaryotic microbes (fungi and algae), and the roles they have played in shaping terrestrial ecosystems and nutrient-cycling over geologic timescales. Both avenues of his research attempt to link diverse fields and organismal groups. He also has conducted work addressing the timing and evolutionary consequences of ant-plant interactions. Matt thank you so much for joining us on the Mushroom Hour!    TOPICS COVERED:     Fungus & Algae Species Forming Lichen Partnerships    Host Specificity in Lichen Partnerships    Evolutionary History of Lichen    Vascular Plants on Land Before Lichen?!    Challenges of Working on “Big Time”    Process of Lichen Formation, Fungal Phenotypes    Lichen Blurring Species Boundaries    Cleptobiosis    Role in Carbon & Nitrogen Cycles    Lichen as an Ecosystem    Lichen & Air Quality in an Environment    Lichenometry   Analysis of Fungal Coal Formation Hypothesis    Ant Plant Interactions   EPISODE RESOURCES:    Matthew Nelsen Website: https://mpnelsen.com/   Lichen: https://en.wikipedia.org/wiki/Lichen   Xanthoria parietina (Lichen): https://www.wikiwand.com/en/Xanthoria_parietina   Trebouxia (Lichen Genus): https://en.wikipedia.org/wiki/Trebouxia   Toby Spribille (Lichen Expert): https://scholar.google.com/citations?user=vPlIL5IAAAAJ&hl=en   Betsy Arnold (Endophyte Expert): http://www.arnoldlab.net/   Article on Fungal Coal Formation Hypothesis: https://www.pnas.org/doi/10.1073/pnas.1517943113  Arthrobotrys (Fungal Genus): https://en.wikipedia.org/wiki/Arthrobotrys   Mycoparasites: https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/mycoparasites