A New Frog Hiding in Plain Sight Is Found in the Amazon's Flooded Forests

A small frog living in a flooded corner of the western Brazilian Amazon has turned out to be a species scientists had never formally recognised. Named Adenomera varcena, it looks so much like its close relatives that appearance alone could not set it apart. Its identity emerged only after researchers combined DNA evidence, recordings of its mating call, physical measurements, comparisons with museum specimens and details of its habitat.

Researchers encountered the frog during expeditions in the Upper Juruá River region of Acre, near the Moa and Crôa rivers and the city of Cruzeiro do Sul. Its name refers to várzea forests, the Amazonian floodplains that are periodically submerged as rivers rise. Most closely related Adenomera frogs live in terra firme forests, areas that stay above seasonal floodwaters, so the new species widens the range of environments the group is known to occupy.

Flooding is not just a passing disturbance in várzea forests; it is one of the forces that define them, repeatedly changing which parts of the forest floor animals can reach. For a small frog whose reproduction depends on local conditions, that makes its choice of habitat especially important.

The discovery highlights what scientists call cryptic diversity, where animals that look nearly identical belong to separate evolutionary lineages, so visual identification alone can miss species hiding in collections or field records for years. A. varcena belongs to the Adenomera simonstuarti species complex, a western Amazonian group that genetic research had already shown contains several distinct lineages. Identifying new species also feeds directly into conservation planning.