Adjunct Professor Greg Mueller is a fun guy. Image courtesy of Greg Mueller.

“I just ate this mushroom. What is it?”

Greg Mueller sighs. “It’s always a guy,” he says in an exaggerated whisper. “I say, ‘Why didn’t you call me before you ate it?’”

Mueller, an adjunct professor at Northwestern University and one of Chicago’s top mycologists (AKA fungus experts), receives several calls a week from daredevil dudes, panicked parents, pet owners and the occasional hallucinator who find him listed as a resource on websites like the North American Mycological Association’s. But volunteering as a mushroom toxicity consultant is just a side gig to his full-time role as the Chicago Botanic Garden’s chief scientist. There, he oversees research, teaching and community outreach programs and tries to get people to care about fungi for reasons other than potential poisonings. As it turns out, their benefits are as plentiful as the mushrooms popping up across Chicago this rainy fall.

Growing up, Mueller and his four brothers went camping near their home in southern Illinois and in national parks around the country. While convenient family vacations – “That’s what you could do when you had five boys,” Mueller says – these outdoor adventures planted the seed that blossomed into his lifelong love of plants.

Mueller earned his bachelor’s and master’s degree in botany at Southern Illinois University Carbondale and received his Ph.D. in botany from the University of Tennessee. He decided to study fungi, “something that was a little different,” he says. “There’s a million people working on orchids, but not many people working on this. And [fungi are] super important.”

Fungi act as recyclers, breaking down dead plant material that litters the forest floor and serves as kindling for wildfires. Some cause disease, killing old or weak trees and making space for new ones to grow. “In a natural system, pathogens aren’t necessarily bad,” Mueller says. “They’re doing their job keeping good age demographics.”

Mueller specializes in a type of fungus that grows inside or attached to a plant root. It uses its mycelium – a network of tiny tubes extending many feet into the soil – to help the tree or shrub forage for water and nutrients. In return, the plant provides the fungus with sugar it makes during photosynthesis. By consuming the sugar, the fungus sequesters the carbon source deep underground, preventing it from leaching back out into the atmosphere.

Still, some fungi are struggling to thrive in habitats stressed by climate change. Mushroom species that gradually migrate to higher elevations in search of cooler temperatures will eventually “run out of real estate up on top,” Mueller says. Changing rainfall patterns also jeopardize fungi accustomed to certain levels of moisture.

In 2014, Mueller began documenting threatened mushrooms with the Global Fungal Red List Initiative, a project that consolidates fungus photos captured by citizen scientists throughout the world. He sometimes issues “rare challenges,” tasking participants with sighting a shy ‘shroom. The number of species on the red list has skyrocketed from three to 545 in the past seven years, but that’s largely because of the expanding team of contributors.

To define the boundaries between different breeds of fungi, Mueller collects samples and analyzes their DNA. He has discovered over 30 new species that grow in unique regions, guiding efforts to preserve biodiversity. “Now that we know that we have a discrete suite of species that occur only here in the Midwest,” Mueller says, “all of a sudden, we need to be thinking about conservation status.”

When he’s not studying them, Mueller enjoys eating the fungi he gathers. “One for the frying pan, two for the collection,” he says. He welcomes store-bought varieties on his plate as well, ordering mushrooms on his pizza “every time.”

Adding to his metaphorical plate, Mueller advises graduate student researchers in the Program in Plant Biology and Conservation, a collaboration between the Chicago Botanic Garden and Northwestern University. Willow Abshire Sims, one of Mueller’s master’s students, proposed an experiment to see how far the “wood wide web,” a system of communication between trees through mycelium, could extend. She says Mueller supported her plan to grow and observe five pine saplings and their fungi friends in the lab, even though other studies had only looked at two trees. “It never felt like, ‘This can’t work. You can’t do it that way,’” she says. “It was always like, ‘Let’s figure out how that could work.’” Mueller also mentors students in Central and South America, teaching virtual classes, raising funds to support graduate-level researchers and serving on Ph.D. committees.

Mueller is known for his mycology memorabilia, including a Christmas tree decorated exclusively in mushroom ornaments and a hat made from the soft fibers of a hoof-shaped fungus called Fomes fomentarius. “It’s always fun to see all those things and how excited he has remained about science, conservation and fungi over the decades of time that he’s been in the field,” says Nyree Zerega, the Director of the Program in Plant Biology and Conservation. Mueller’s enthusiasm inspires Zerega’s own curiosity and helps the public understand and appreciate an often overlooked part of the environment, she says.

“I say I work with fungi and people kind of look at you like, ‘Oh, isn’t that cute,’” Mueller says. “Versus now, we’re finally getting to the point that I’ve got journalists coming in to interview me. So that’s progress.”