Seven new species of miniature frog have been discovered on seven different mountains in south-eastern Brazil.
The cool "cloud forests" of this region have a unique climate, separated by warmer valleys that isolate the peaks like islands.
That isolation has produced 21 known species of Brachycephalus frog - and the new arrivals push that count to 28.
All are less than 1cm long and many have colourful, poisonous skin to help them avoid becoming tiny meals.
The newly discovered species, reported in the open-access journal PeerJ, are the fruit of five years of expeditions into the wilderness.
The high forests near Brazil's southern Atlantic coast are a fertile place for ecologists to explore, Marcio Pie, a professor at the Federal University of Parana in nearby Curitiba, told the BBC.
Prof Pie said the cloud forests yielded more different species per square kilometre than the Amazon.
For animals like the Bracycephalus frogs that are particularly sensitive to their environment, even the temperature change from mountain to valley forms a barrier.
That leaves the population on each mountain top to slowly develop into a separate species.
As some of the very smallest land-dwelling vertebrates, much of their anatomy is optimised to their tiny scale. For example, they typically have three toes and two fingers, instead of the five toes and four fingers found in most frogs.
The most obvious differences between Brachycephalus species, including the seven new ones, is their skin.
This can vary quite a lot in how bumpy and rough it is, and quite dramatically in its colour - with more vibrant tones normally reflecting higher levels of the deadly chemical tetrodotoxin.
After catching enough specimens, which usually involved rifling through leaf litter with their bare hands, Prof Pie's team also did genetic tests to describe each new species.
Finding them in the first place was probably the biggest challenge, he said.
Often the researchers would hear the frogs long before they saw them, but the creatures, whose principal predators are probably snakes, tend not to give away their location easily.
"You can hear them singing and there's probably hundreds of them, but you simply can't catch them! Because once you get closer, just from the vibration in the ground, they keep silent for, say, 20 minutes or half an hour. And then you have to go through the leaf litter very carefully with your hands," Prof Pie said.
The unique climatic pockets of the cloud forests are vulnerable, the scientists say. The presence of the frogs within such small geographical ranges suggested this particular area had been pretty stable for last the past 500,000 years, in terms of the climate.
Prof Pie and his colleagues warn that keeping this remarkable variety of species alive may require captive breeding, as well as efforts to protect their habitat from invasive plant and animal species, logging, and other threats.