Amidst the jagged, vast Pyrenees, a little green herb with heart-shaped leaves clings to just two adjacent cliff sides. That's the worldwide geographic range of Borderea chouardii. The site is so inaccessible that the species was only discovered in the 1950s. For the past 18 years ecologist María Begoña García has clambered up scaffolds to check in on each specimen.

It turns out that the plant's reproductive strategy is just as eccentric as its location, making its survival even more perilous. Many of the seeds simply fall to the ground near the mother plant. But a substantial portion are dispersed by ants, which carry the seeds to new locations while bumbling along the cliffs.

The meandering ants also pollinate B. chouardii, making this an instance of "double mutualism," or a relationship in which one species relies on another to fulfill two roles. So what do the ants get out of this? They haul each seed back to their nest so larvae can dine on its elaiosome—a fatty, fleshy coating. After the feast the intact seed is dumped outside like garbage where it may eventually grow into a full plant. García, of the Spanish National Research Council, along with colleagues from the Autonomous University of Barcelona and Aarhus University in Denmark have identified three ant species that participate in this process: Lasius grandis, L. cinereus and Pheidole pallidula. The team's complete study of the plant was detailed in PLoS ONE on September 12.

Given this strange pollination and seed-dispersal strategy, it is especially impressive that B. chouardii and its ilk have inhabited the Pyrenees for roughly 10 million years, if not longer. The secret to the plant's perpetuity? Each one can live more than 300 years. —Daisy Yuhas