A new study has found that the horsetail plant (Equisetum), a lineage that has existed on Earth for over 400 million years, produces internal water with an oxygen isotope signature so unusual that scientists say it resembles material more commonly associated with extraterrestrial samples.
Researchers reported that water moving through the hollow stems of the plant showed an extreme shift in oxygen isotope composition from the base to the tip. At the upper sections, evaporation had enriched the water so strongly in heavier oxygen isotopes that it exceeded any previously recorded value in terrestrial materials.
The study, led by scientists at the University of New Mexico, shows that this transformation happens entirely within the plant’s stem as water rises upward and evaporates. As lighter water molecules escape into the air more easily, the remaining water becomes progressively “heavier” in its isotopic makeup. This process intensifies along the plant’s height, producing a steep chemical gradient.
According to researchers, the measurements were so unusual that the final isotope signature would be difficult to distinguish from material that might originate from a meteorite. The finding highlights how powerful evaporation alone can be in reshaping the chemical identity of water, even within a living plant.
The research also sheds light on how plants record environmental conditions. Horsetails are known for their high silica content, forming microscopic structures called phytoliths that can persist in soils long after the plant dies. Scientists found that the isotope signature preserved in these structures does not always match the actual water moving through the plant, suggesting that fossil based climate reconstructions may need to be carefully re-evaluated.
This mismatch is important because phytoliths are widely used to reconstruct past humidity and climate conditions. If evaporation inside plants can distort isotope signals so strongly, it could introduce uncertainties into interpretations of ancient environments, including those from millions of years ago.
Researchers say the findings do not undermine climate reconstruction methods, but they do refine them. Existing models of plant water movement and evaporation will need adjustments to better reflect how water behaves under dry, high evaporation conditions.
Because horsetails have existed since the Devonian period, their modern water chemistry may also help scientists better understand ancient ecosystems. By refining isotope models, researchers hope to improve reconstructions of prehistoric humidity levels and environmental conditions.
The study adds to growing evidence that simple physical processes like evaporation can create extremely complex chemical signatures inside living organisms sometimes pushing Earth based materials into ranges previously thought to be almost impossible outside extraterrestrial environments.