Nine new species of bush frog have been discovered in the Western Ghats, a mountainous region in southern India that is a hotspot of biodiversity.

Bush frogs are tiny animals, found mainly in South and South-East Asia, some of which can fit onto a 20 pence coin. Beginning in 2008, S. P. Vijayakumar, then at the Indian Institute of Science in Bangalore, has been scouring the Western Ghats to find them. The new species he has found all belong to the genus Raorchestes, and he has identified them based on their appearance and genetics. Vijayakumar and his colleagues have published their findings in Zootaxa.

The Western Ghats is home to many species of frog, including the 14 dancing frogs discovered earlier this year. That's because it is a fragmented landscape, with hills, valleys and plateaus. This means populations of frogs can easily wind up evolving in isolation. "Small species, in particular, are not able to move very far and have a smaller habitat," says co-author Kartik Shanker of the Indian Institute of Science in Bangalore. He expected to "find a new species in every hill range".

R. flaviocularis was discovered perched on the leaves of short trees in a disturbed forest fragment within a tea estate. It is easily discernible, thanks to the metallic-yellow patches on its eyes. It is hard to locate, because its calls seem to originate from somewhere other than their actual source.

R. aureus has, er, eye-catching golden eyes, surrounded by speckles. The species was found in 2010 in grasslands on the edge of a forest.

R. primarrumpfi prefers to live in grasslands and swamps at high elevations. Its eyes have a distinctive shimmering golden-silver arc. Its peculiar name is derived from the German word "Primarrumpf". This refers to Gondwanaland, a giant continent that once existed on Earth, remnants of which can be found in the Western Ghats.

This little fella has horn-like ridges on its back, and its eyes are speckled gold with a brown band on the lower edge. R. echinatus shows a strong preference for grasslands and was first spotted perched on grass blades in 2011.

At about 5 cm long, R. emeraldi is the largest Raorchestes species known. It has fleshy purplish armpits, and yellow spots scattered here and there.

Found along the edges of wet evergreen forests on shrubs and grasses, R. leucolatus spends most of its time in the forest understory. It is mostly a dark brownish-red with white spots, but also has conspicuous white patches on its groin.

First spotted in wet evergreen forests in 2010, R. archeos is a light brown, medium-sized bush frog. It is mottled on the underside and has a distinct golden-brown eye colour. For some unknown reason, half its arms are black and the other half brown.

A forest-dwelling bush frog species found in the understory shrubs, R. blandus is named after its melodious mating calls: the Latin word "bland" means "pleasant". It has prominent and irregular reddish-brown glandular patches on its skin and was first spotted in 2008.

R. indigo is named after the patches of indigo on the underside of its legs. It was found on leaves on the forest floor of Kudremukh, a mountain peak that has an uncanny resemblance to a horse's face.

There are now known to be 52 species of Raorchestes in the Western Ghats. Vijayakumar and his team saw all of them during their expedition. They also found 13 genetically distinct and geographically-isolated populations of bush frogs. They suspect these are new species but have not yet named or described them in detail, says Vijayakumar, who is now at the National Centre for Biological Sciences in Bangalore.