As soon as I saw that, I knew we had something really interesting
Beneath the surface of desert moss, a doctoral researcher at UC Riverside has found what science long insisted was not there — fungi living inside the leaf cells of a common Mojave species, forming branching structures nearly identical to the nutrient-exchange organs found in plant roots. For decades, mosses were considered the lone exception to a fungal partnership that sustains 99 percent of land plants, a relationship stretching back 470 million years to the first colonization of dry land. This discovery does not merely add a footnote to botany — it reopens the question of how life first learned to endure the terrestrial world, and suggests that thousands of moss species may carry hidden alliances we have never thought to look for.
- A doctoral researcher spotted branching fungal structures inside desert moss cells — structures that, by the prevailing scientific consensus, had no business being there.
- The find challenges decades of botanical certainty: mosses were the one group of land plants believed to survive without fungal partners, and that assumption is now cracking.
- Surface-sterilized samples and DNA analysis confirmed the fungi were living inside the moss tissue itself, not contaminating it from surrounding soil — and the organisms found cannot survive without a living plant host.
- Arid desert sites showed far fewer of these intracellular structures than cooler coastal ones, raising an urgent warning: as the American West dries and heats, the fungal communities inside moss may collapse, taking their drought tolerance with them.
- Before the relationship can be formally called a symbiosis, researchers must prove nutrients are actually exchanged — and then face the larger task of searching more than 10,000 known moss species that have never been examined for fungi within their cells.
Kian Kelly was peering through a microscope at desert moss when he noticed something that contradicted decades of botanical understanding. Inside the leaf cells of Trichostomopsis australaceae — a moss common to the Mojave and Sonoran deserts — were delicate, branching fungal structures nearly identical to the nutrient-exchange organs found in plant roots. Kelly, a doctoral researcher at UC Riverside, recognized immediately that he was looking at something the field had long said did not exist.
The partnership he suspected belongs to a class of fungi called arbuscular mycorrhizal fungi, or AMF — organisms that sustain roughly 99 percent of all land plants by trading soil-drawn phosphorus and nitrogen for plant-produced sugars. This arrangement is thought to have made it possible for plants to colonize dry land some 470 million years ago. Mosses had always been treated as the exception, believed to draw what they needed from air and rain without any fungal assistance.
Working with microbiology professor Jason Stajich, Kelly collected moss from volcanic rock fields and granitic soils across the Mojave and Sonoran deserts, as well as from cooler coastal sites near San Diego. After surface-sterilizing each sample to remove external organisms, they searched the tissue for fungal DNA. What they found inside the moss was distinct from the fungi in surrounding bare soil — and included AMF, which cannot survive without a living plant host. A chemical stain confirmed the branching structures were present inside the leaf cells themselves.
The variation across climate zones added another layer of significance. Desert samples contained far fewer of these intracellular structures than coastal ones, leading Kelly to suspect that certain fungi help moss endure heat and drought — and raising the question of what happens to that protection as the American West grows more arid.
Mosses are close relatives of Earth's earliest land plants, the pioneers that first moved from water to dry ground. If fungi helped those ancient ancestors make that transition, mosses may have been part of that story all along. Confirming the relationship as a true symbiosis will require demonstrating that nutrients actually move between moss and fungus, not just that the structures are present. And beyond that lies a larger frontier: more than 10,000 known moss species have never been examined for fungi living inside their tissues. The study, published in New Phytologist, suggests many more hidden partnerships may be waiting.
Kian Kelly was looking at desert moss under a microscope when he saw something that shouldn't have been there. Inside the leaf cells of Trichostomopsis australaceae, a common moss from the Mojave and Sonoran deserts, were branching fungal structures—delicate, repeated networks that looked almost exactly like the nutrient-exchange organs found in plant roots. "As soon as I saw that, I knew we had something really interesting," Kelly, a doctoral researcher at the University of California, Riverside, said later. What he had found was a partnership that science had spent decades insisting did not exist.
For generations, botanists have understood that nearly all land plants—roughly 99 percent of them—depend on fungi to survive. These organisms, called arbuscular mycorrhizal fungi, or AMF, burrow into plant roots and trade phosphorus and nitrogen pulled from the soil for sugars the plant manufactures through photosynthesis. It is one of Earth's most fundamental biological arrangements, a handshake between kingdoms that made it possible for plants to colonize dry land in the first place, some 470 million years ago. Mosses, though, were always treated as the exception. They were thought to get by alone, drawing what they needed from air and rain, asking nothing of the fungal world beneath them.
Kelly and his co-author, Jason Stajich, a microbiology professor at UCR, set out to test that assumption. They collected moss samples from the volcanic rock fields and granitic soils of the Mojave and Sonoran deserts, where summer temperatures regularly exceed 100 degrees, as well as from cooler, wetter coastal sites near San Diego. Back in the lab, they surface-sterilized each sample to strip away external organisms, then ground up the tissue and searched for fungal DNA. What they found inside the sterilized moss was distinct from what appeared in bare soil collected just inches away. Among the fungi present were AMF—organisms that cannot survive without a living plant host. Their presence inside the moss tissue was not accidental contamination. Something was keeping them alive.
To confirm that the fungi were actually living inside the plant cells, Kelly used a chemical stain that binds to fungal tissue and examined the samples under magnification. Inside the leaf cells of the desert moss, he saw branching structures that researchers now call "arbuscule-like"—similar in form to the nutrient-exchange organs that AMF builds inside the roots of other plants. No prior study had documented this kind of intracellular branching inside healthy moss cells. The structural evidence suggested that moss and fungus were engaged in the same kind of nutrient exchange that sustains the vast majority of land plants.
What made the finding even more striking was the variation across climate zones. Moss samples from the arid Mojave Desert contained far lower concentrations of AMF than those from the coastal sites, and the intracellular structures visible at the coast were absent in the driest material. "We suspect that certain fungi are more helpful for surviving hotter, drier climates," Kelly said. This raised an urgent question: as the American West grows hotter and drier, will the fungal communities inside desert moss shift in ways that undermine the moss's ability to withstand heat and drought?
Mosses are closely related to some of Earth's earliest land plants—the pioneers that first moved from water to dry ground. If fungi helped those ancient ancestors make that transition, as evolutionary evidence suggests, then mosses may have been part of that story all along, written out by later assumptions. This discovery puts them back in. Before the relationship can officially be called a symbiosis, researchers need to demonstrate that nutrients are actually moving between moss and fungus. The structural evidence is consistent with that exchange, but observation alone is not enough. What comes next is verification, and then the harder work: examining the more than 10,000 known moss species, nearly all of which have never been searched for fungi living inside their tissues. The study, published in the journal New Phytologist, suggests there may be many more hidden partnerships waiting to be found.
Notable Quotes
That's been the model. Mosses, the thinking went, simply didn't engage with fungi.— Jason Stajich, professor of microbiology and plant pathology at UC Riverside
We suspect that certain fungi are more helpful for surviving hotter, drier climates.— Kian Kelly, doctoral researcher at UC Riverside
The Hearth Conversation Another angle on the story
Why does it matter if moss has fungi inside it? Isn't that just a detail about one plant?
Because it rewrites when and how life colonized land. If mosses—which are ancient plants—have always had fungal partners, then that partnership is older than we thought. It changes the whole timeline of plant evolution.
But you said the fungi are only present in some mosses, not all of them. Doesn't that suggest it's a recent development, not ancient?
That's the puzzle. The fungi are there, but they're more abundant in wetter climates and less visible in the driest deserts. It suggests the relationship adapts to conditions. The question is whether it's always been there, just changing form, or whether it's something newer.
What happens if those fungi disappear as the climate changes?
The moss loses a source of nutrients it may have come to depend on. In a desert already stressed by heat and drought, that could cascade—less stable soil, more erosion, more dust. The biocrust communities that hold drylands together become fragile.
So this discovery is actually a warning?
It's both. It's a discovery about the deep past—how life adapted to land. But it's also a window into a future we're not prepared for. We're only now learning what these partnerships are. We don't yet know how to protect them.