A team of 99 researchers from institutions across the globe, including The University of Western Australia, completed the comprehensive study of flora on the island.
They found that New Guinea had 13,634 recognised species of plants, earning it the title of most the botanically diverse island in the world.
New Guinea is the world’s second largest island after Greenland, and is made up of both Papua New Guinea to the east and Indonesia to the west.
It is one of the last three tropical wilderness areas in the world with around 70 per cent of its original forest cover intact.
"This is the most mega-diverse island, from a floristic perspective, with 68 per cent of plants only found in the region, which is unmatched in tropical Asia."Associate Professor Bruce Webber
The study, published in Nature, found that the island had 19 per cent more species than Madagascar and 22 per cent more species than Borneo.
One reason for this diversity is its wide range of climates and ecosystems, which includes lowland mangroves on the coast rising to tropical alpine grasslands and a glacier on the 5030m mountain, Puncak Jaya.
The island’s plant specimens extend from herbs that produce some of the world’s largest bananas to orchids with appendages that look like spiders.
The study is an important step towards improving the conservation of the region’s unique biodiversity.
Associate Professor Bruce Webber from UWA’s School of Biological Sciences and CSIRO said it was the first attempt to critically catalogue the entire vascular plant diversity of New Guinea.
“This is the most mega-diverse island, from a floristic perspective, with 68 per cent of plants only found in the region, which is unmatched in tropical Asia," Dr Webber said.
“In an area so varied and poorly sampled, it is likely there are many more plants on New Guinea that are undescribed and unknown to western science.”
However, Dr Webber said the island's floral diversity was increasingly under threat from logging, mining and conversion of forests for subsistence agriculture.
“This is the most concerning part of the work for me,” Dr Webber said. “It's likely that we're losing plants before we even know they exist.
“Conserving New Guinea’s unique flora will be no easy task but this is a globally important challenge that we must grasp with both hands.