Rebecca Yahr

There’s a toolkit that Rebecca Yahr takes with her on field trips that sounds more suited to a surgeon, or a sculptor. It contains a couple of carbide-tipped chisels, knee pads and DIY gloves. A sharp fixed-blade knife and a junk knife for soil. A saw. “I’m prepared for every eventuality,” Rebecca – known as Becky – says as we duck to avoid low branches at the Royal Botanic Garden Edinburgh, a majestic, gentle 70-acre hillside of greenery and elegant Victorian glasshouses with views across to Edinburgh Castle. “But it depends on the trip. If I’m going to the top of a mountain, I’m not going to take a saw.”

Fused onto slabs of granite or sprouting in tangles from an ancient oak tree, the objects of Becky’s quests are lichens. She has hunted them in the Colombian tropics, sawing off branches laden with little-known species, and at the top of the snowy Cairngorms. But she also leads “lichen safari” trips for the public around the Botanics, as the gardens are known, explaining to curious visitors that they are neither a sign of decay nor a horticulturalist’s pest. “I often get asked, ‘How do you get rid of it? Is it killing my azaleas?’”

American-born Becky is the lichen biodiversity scientist here, and her role is to identify and conserve these charismatic organisms across the Botanics’ four main sites in Scotland (besides Edinburgh, there are Benmore and its redwoods, the Gulf Stream-warmed garden at Logan, and hilly Dawyck in the Borders) to expand knowledge of them and to flag those in danger via her work for the International Union for Conservation of Nature, which maintains the Red List of Threatened Species. At the same time, she is contributing genetic samples to the Darwin Tree of Life Project, a hugely ambitious 20-year programme that aims to create an inventory of the entire genomes of all animals, plants and fungi in Britain and Ireland.

Lichens, of which about 1,900 species have been identified in the UK, are both familiar by sight and widely misunderstood. On the one hand, they seem indestructible, surviving inside solid rock, in deserts and in the Antarctic. In 2005, Russian scientists blasted a sample into orbit, and it survived for 15 days in the vacuum of space, returning to earth unaffected. Rootless and hardy, lichens have been admired by humans for centuries for their perceived steadfastness. “Of what a strange nature is knowledge!” Mary Shelley wrote in Frankenstein. “It clings to the mind, when it has once seized on it, like a lichen on the rock.”

Yet they are highly vulnerable to the pollution we cause. During the Industrial Revolution they were all but wiped out in the UK. Becky shows me a carpet of springy black dog lichen (Peltigera canina) on rocks in an Alpine garden. These plants’ presence here hasn’t always been guaranteed. In the 1970s, she says, you would have been lucky to spot a lichen in the gardens; now they flourish.

Quite apart from their function as nature’s canary in the coal mine, they are perplexing. A lichen isn’t even a single life form but a combination of loving partners: firstly a fungus, which provides the physical structure, and then, living within it, an alga. In exchange for shelter, the alga offers photosynthesis, making energy for the fungus. To complicate things, sometimes the photosynthesising partner is not an alga but a bacterium, cyanobacterium, and sometimes all three are in the ménage. The word “symbiosis” was coined by the German botanist Albert Bernhard Frank in 1877 specifically to describe lichen. “The symbiosis is at the heart of the matter,” Becky says. “It’s eye-opening once you understand that this is not one thing that you are holding in your hand but two things intimately linked that couldn’t live without each other. That’s how people start to appreciate them. They start to understand just how interlinked things are.”

It is only since the late 19th century that this cosy relationship has been understood. The scrambled-egg-coloured crusty patches you might see on a gravestone and the frothy reindeer lichen that look like dolly-sized shrubs were for centuries ascribed to the world of fungi, a separate kingdom. Carl Linnaeus, the 18th-century genius who invented the system of Latin nomenclature that describes all living things, was unable to comprehend them. “He wasn’t interested in lichens,” Becky says. “He just said, ‘I’m going to let them alone, call it all lichen and be done with it. It wasn’t until [Simon] Schwendener came around in 1867 and had a look inside, saw those little green balls and said, ‘You know, they look a lot like algae, don’t they? This is algae, and this is a symbiosis. Things are working together, and it’s a fundamental aspect of this part of life.’” These days, science can’t get enough of lichens.

The week before I travel to Edinburgh to meet Becky, I watch a YouTube tutorial she made on how to identify the three main lichen “shapes”. Among her many responsibilities is supervising PhD students, but this clip is a basic lesson: Lichenology 101. Sitting in front of a small blackboard in a room in her home in the north of the city, near Granton Harbour, she patiently explains how to spot the “crusty”, “leafy” and “bushy” varieties, drawing simple diagrams of their structures, pausing to take questions from an invisible online audience. “I had molecular training,” she tells me later, “but I prefer doing something where I use my field skills.” During the video, she explains how to use a small magnifying lens to get up close, as a jeweller might to assess a diamond. That way, it’s possible to see how the complex structures of a lichen resemble corals or jigsaw puzzles or teased wool. Her enthusiasm makes you want to pull on a Patagonia fleece and spend hours lying prone in a cemetery.

Becky says that the recent rise of backyard botany – in part due to the restrictions of the pandemic – has led to a renewed interest in lichens, which are small and accessible. Visitors to the Botanics are curious. “On the safaris, for instance, what we want to do is tell stories. I could just tell you the names of the different lichens, but nobody wants that, right? There are stories, for instance about how sensitive they are to air pollution. Some fix nitrogen from the atmosphere, just like legumes do in the soil. Did you know that lichens do that?”

Communicating with the general public is taken far more seriously by academia now than it was a decade ago. “When I did my PhD in the early 2000s, science communication didn’t exist; it wasn’t a field,” Becky says. “Nowadays, you can’t do a doctorate without actively thinking about how you’re going to communicate it. Public communication is a critical part of what we do. This happened clearly with Covid, right? If we can’t talk about it, then nobody understands what is happening. It’s the same with conservation, with biodiversity, with everything. So we’ve become a bit more savvy about talking about what we do.”

If Becky, 50, is a persuasive speaker on her subject, that might be a talent inherited from her late father, Barry Yahr. He was a sales rep for furniture companies, “as was his brother, and his dad had a furniture store. They all had the gift of the gab, and I hope a little of that rubbed off on me.” She grew up in Georgia, in the foothills of the Appalachian Mountains. “Extensive oak, pine and hickory woods” is how she describes the landscape, “third-, fourth- or fifth-growth forest. It’s been cut and cut and cut. There’s nothing special about the forest where I grew up; it just goes on and on.”

Her artist mother, Monica Yahr, is “nature-loving”, and the family took road trips across the USA in their RV, visiting national parks, and 48 states in total by the time Becky was 18. (“I’m missing two: Utah in the lower 48, plus Alaska. We did lots of road trips.”) Meanwhile, her own interest in botany was blossoming, if as yet unidentified. “I used to go down to the river by myself all the time, nominally fishing,” she says. “You know how old guys who fish wear waistcoats with lots of pockets? I had one, and I filled the pockets with field guides, magnifying glasses, tweezers – nerd stuff. Not tackle. I loved fishing, but I was never good at it, and at some point I asked myself, Am I doing this for the fishing or because I like being in the woods and learning all the plants? I was teaching myself botany.”

By the time Becky was an undergraduate at the University of California, Davis, in the 1990s, she was back out into the field, this time in the middle of the desert, to count rare plants in remote locations. Her boss was Maile Neel, a conservation botanist who at that time ran the US Forest Service’s field crew. Becky calls Neel “one of my absolute heroes. She gave me a huge amount of responsibility. She gave us, a group of undergraduates, a truck, a set of keys, a compass and said, ‘Good luck!’ I’m amazed we ever got back from some of those days.” Neel was the person who made Becky realise she was “a Botanist with a capital B. I wasn’t confident in myself until I had that job.” Neel remembers Becky as an “already accomplished field botanist with a commitment to conservation”, she tells me by email. “And through her work now, she has a global impact on the conservation of these critical species, while teaching others how critical they are to our ecosystems. And beyond her technical skills, she was always wise beyond her years. I would follow her anywhere.”

Botany, Becky believes, isn’t one of the areas of science where women are obviously outnumbered. “We have a lot of gay men and a lot of women. There are straight men too, but they’re in the minority. That seems to be the way it is. It’s true that I never struggled with [sexism]. I don’t think I became aware of it until I was doing my PhD; then it became clearer. At that level in the academics, you see fewer women in the authority roles. But in the early steps in botany, I don’t think you run into it so much.”