Miniature wetlands that form on the branches of tropical trees emit methane, a potent greenhouse gas, suggests a study published online this week in Nature Geoscience. Tropical forests are thought to emit large quantities of methane to the atmosphere, but the source of the gas has remained uncertain.

Edzo Veldkamp and colleagues collected plants that grow on the branches of tropical trees — known as tank bromeliads — in the Ecuadorian Andes, and measured their methane emissions. All plants emitted methane, due to the accumulation of methane-producing microbes in water-filled tank-like structures at the base of their leaves.

The authors suggest that the plants act as miniature wetlands and, together with other wetlands hidden beneath the forest canopy, could help to explain the high methane levels above tropical forests. In an accompanying News and Views, Joseph B. Yavitt writes, “Hopefully, the work will spur the search for cryptic wetlands lurking in other remote places. Personally, I believe that we have missed many obscure wetlands out there and they are waiting to be discovered.”