The finding comes as logging, mining, and agriculture increasingly threaten the island’s forests, which are vital to the world’s carbon sequestration needs.
Led by Dr Rodrigo Cámara-Leret from the University of Zurich, the study involved 99 researchers from across the globe, including Dr Bruce Webber from Australia's national science agency, CSIRO, and was published this week in Nature.
New Guinea is the world’s second largest island after Greenland, and is part of both Papua New Guinea to the east and Indonesia to the west.
The study found that the island had 19 per cent more species than Madagascar and 22 per cent more species than Borneo across its varied climate, which includes lowland mangroves rising to tropical alpine grasslands and a glacier on the 5030m mountain, Puncak Jaya.
Dr Webber said this 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, 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.
Dr Cámara-Leret said because nearly 70 per cent of the flora was endemic, it was important to document and understand the region.
"New Guinea's flora is also globally important because, along with the Amazon and the Congo, it is one of the last three tropical wilderness areas with around 70 75 per cent of its original forest cover intact," Dr Cámara-Leret said.
"Therefore, it has a major role in carbon dioxide sequestration.
"Indigenous communities domesticated some of the most important plants that are eaten today, including the banana and sugar cane, and have discovered a wide range of uses of other plants.
"Looking after the plants of New Guinea is important for supporting local livelihoods. Some of the authors of this paper are actively involved in working with policy makers to help Indigenous communities preserve their forests."
The paper is temporarily free to access here: New Guinea has the world’s richest island flora [pdf · 7mb]
And can then be accessed here: Nature - New Guinea has the world’s richest island flora
- This work was enabled by the study of plant specimens in herbarium collections around the world, including the Australian National Herbarium (ANH).
- The ANH collection houses thousands of plant specimens that were collected in New Guinea from the 1950s up until the present day. They reveal the biodiversity of the island.
- During the past year, staff at the herbarium have given scientific names to five new species from New Guinea, including four that are related lilly pillies and one rainforest shrub.
- The Australian National Herbarium is part of the Centre for Australian National Biodiversity Research, a joint venture between the Department of the Environment's Parks Australia Division and CSIRO.
