The vast area of forest in northern Mozambique was first noticed by the Kew team on Google Earth. The botanic garden is working with Mozambique's government to identify priority areas for conservation.
Local conservationist Julian Bayliss investigated the "unexpected patch of green" and used satellite photos to identify the 7,000ha forest in the Mount Mabu region.
The area was known to villagers nearby but had never been explored by scientists. The country's civil war and poor access to the forest are believed to have helped protect it.
An international team of 28 scientists and support staff from the UK, Mozambique, Malawi, Tanzania, Belgium and Switzerland hiked into the area in October and November of last year.
During the three-week expedition the scientists uncovered three new species of butterfly and a new snake. They believe they may have two new species of plant among the 500 specimens collected but this has yet to be verified.
The expedition leader, Kew botanist Jonathan Timberlake, said: "The phenomenal diversity is just mind-boggling. It is potentially the biggest area of medium-altitude forest I'm aware of in southern Africa and by conserving the plant life we can help secure a future for all the other creatures we saw there."
The expedition was led by Royal Botanic Gardens, Kew, working with colleagues from the Mozambique National Institute of Agronomic Research, Birdlife International and the Mulanji Mountain Conservation Trust in Malawi.
- Kew gardens attracted 25,000 people to the free launch of its 250th year on 1 January.