These fungi formed partnerships with the first land plants 450 million years ago, enabling plants to colonize land. Over 90% of modern plants still depend on these ancient fungal networks that predate the evolution of roots.
The partnership that built a green planet
In a field in Aberdeenshire, Scotland, lies evidence of a revolutionary partnership that allowed life to conquer the continents. It is called the Rhynie chert, a sedimentary rock deposit dating back 407 million years to the Early Devonian period. This deposit contains the world's most perfectly preserved early terrestrial ecosystem, fossilized in stunning detail by silica-rich water from ancient hot springs. The environment would have resembled a volcanic area, similar to modern-day Yellowstone National Park, with geysers and geothermal pools.
Within this chert, scientists have found the fossilized remains of the first simple land plants, such as Aglaophyton major. These plants were leafless, stood only about 15 cm high, and importantly, had no roots. So how did they absorb nutrients and water from the harsh, rocky ground? The answer is inside their fossilized stems: microscopic fungi.
The fossils show fungal hyphae—tiny thread-like structures—penetrating the plant's cells, forming structures almost identical to the arbuscular mycorrhizal fungi that associate with over 90% of plants today. This was a symbiotic relationship. The fungus, from the ancient phylum Glomeromycota, acted as a root system, drawing in water and minerals like phosphorus from the soil. In return, the plant, capable of photosynthesis, provided the fungus with sugars and carbon. This exchange was so effective that it has remained one of the most widespread and important symbioses on the planet for over 400 million years.
Evidence of deep time
The preservation at Rhynie is so exceptional that individual cells and even the delicate, tree-shaped structures called arbuscules—the exact sites of nutrient exchange—are visible inside the plant cells. This level of detail confirms the organisms were engaged in a living, symbiotic relationship, not a case of simple decay. The fossils provide the first unequivocal evidence that mechanisms for plant-fungus symbiosis were well established during the Early Devonian.
The discovery of the Rhynie chert was made between 1910 and 1913 by William Mackie, a local doctor and geologist. His find revealed an entire ecosystem frozen in time. Alongside the plants and fungi, the chert also contains some of the earliest known terrestrial animals, including crustaceans, arachnids, and the oldest insects.
The fungi at Rhynie were not limited to symbiotic partnerships. The fossils also show parasitic and saprophytic (decomposer) fungi, indicating that complex fungal roles in the ecosystem had already evolved. Some fossils even show fungi being parasitized by other fungi. The discovery of a new fungal species, Archaeosporites rhyniensis, within the chert in recent years shows that this ancient site yields new information about the foundation of life on land. This lineage is morphologically almost unchanged from its modern relatives in the family Archaeosporaceae, demonstrating a remarkable evolutionary stasis over 400 million years.
💡Fun Facts
The fossils are preserved in three dimensions down to the sub-cellular level by silica from volcanic hot springs.
The early land plant *Aglaophyton* had no true leaves or roots, relying entirely on its fungal partner for nutrient and water absorption from the soil.
The Rhynie chert also contains the fossils of some of the earliest land animals, including primitive spider-like trigonotarbids and springtails.
Some fungal species found in the Rhynie chert, belonging to the Glomeromycota phylum, are strikingly similar to their living descendants today.
The Rhynie chert is a protected Site of Special Scientific Interest (SSSI) located in open pasture. There are no official opening hours, but the fossil-bearing rocks are buried and not accessible for public collection.
Admission
Free. Access is across private farmland.
Accessibility
The site is located in a field with uneven, grassy terrain. It is not wheelchair accessible.