New data reveals New Guinea has the highest plant diversity of any island in the world. Research by botanists from Edinburgh, Kew and the Natural History Museum, in the UK, and the Papua New Guinea University of Technology, Universitas Papua, Papua New Guinea Forest Research Institute and the West Papua Province Regional Research and Development Agency from New Guinea, and other leading research institutes, published today in the journal Nature, presents the first list of all of the plants in New Guinea, the world’s largest tropical island.

The data, compiled by 99 botanists from 56 institutions across 19 countries records 13,634 species of plants from 1742 genera and 264 families, positioning New Guinea as the most floristically diverse island in the world. However, the experts warn, further botanical exploration is urgently needed so species yet unknown to science or presumed extinct can be collected, studied and protected for future generations

This data shows that New Guinea has even more plant diversity than well-known biodiversity hotspot Madagascar (16%), which has 11,488 species recorded.

The authors also found 68% (9,301) of the plants in New Guinea to be endemic to the island, meaning more than two thirds of its plants cannot be found anywhere else. This makes New Guinea the only island in the South East Asian archipelago with more endemic than non-endemic species and is unmatched in tropical Asia. This uniqueness, scientists believe, could be explained by its greater land surface area and habitat diversity, its location marking the junction between South East Asia, Australia and the Pacific, and by having one of the world’s most complex tectonic histories.

New Guinea has fascinated naturalists for centuries. It is home to some of the best-preserved ecosystems on the planet – from mangroves to huge expanses of lowland rainforest to alpine grasslands unmatched elsewhere in the Asia-Pacific region. Botanists have been identifying and naming plants collected in New Guinea since the 17th century, storing the samples in plant collections in herbaria in Papua New Guinea, Indonesia, the Netherlands, and the UK. However, despite notable advances in the past decades in resolving the taxonomy of many New Guinea plants, publications remain scattered, as botanists have previously worked, in the main, independently from each other. Lacking a unifying effort to build a checklist to the region’s plants, great uncertainty remained as to how many plant species grew in New Guinea. Effectively, compared to other areas like the Amazon which has had plant checklists recently published, New Guinea remained the ‘one of the last unknowns for science’.

Dr Peter Wilkie, Head of Sapotaceae Research at the Royal Botanic Garden Edinburgh said: “It is clear, in the context of the biodiversity crisis, that this paper represents a milestone in our understanding of the New Guinea flora and provides a vital platform to accelerate scientific research and conservation. Research at its best is collaborative and this demonstrates what can be achieved when scientists from around the world work together and share expertise and data.

“This checklist is a great starting point but there are still many species awaiting scientific description. Axel Dalberg Poulsen, a world renowned expert on the Ginger family, who undertakes many fieldtrips in New Guinea, with researchers from the island, sums-up the botanical wonder nicely when he advises us to ‘expect the unexpected.’ Begonia researcher Mark Hughes describes his work with botanists from Lae Botanic Garden as ‘a moving target,’ discovering many new begonia species and with only about 25% of them so far having scientific names. There is still much to be revealed.”

Dr Rodrigo Cámara-Leret, lead author and post-doc researcher at the University of Zurich and formerly at the Royal Botanic Gardens, Kew added: “New Guinea is extraordinary: it is a paradise island teeming with life. As the second largest island in the world after Greenland and the world’s largest tropical island, it supports a mosaic of ecosystems and is globally recognised as a centre of biological diversity. However, despite this, knowledge on New Guinea’s flora has remained scattered for years, limiting research in this megadiverse area. Our paper set out to address this.”

In order to solve this great uncertainty around the number of plants known to science on the island, which ranged from 9,000 – 25,000, the 99 botanists verified the identity of over 23,000 plant names from over 704,000 specimens in a large-scale collaborative effort.

They found that New Guinea contains almost three times the vascular plant species of Java (4,598) and 1.4 times the vascular plant species of the Philippines (9,432), the only two large South East Asian island regions with published Floras. Orchids accounted for 20% of the flora in Papua New Guinea and 17% of Indonesian New Guinea, comparable to that in megadiverse countries such as Ecuador (23%) and Colombia (15%) and tree species accounted for 29% of all the flora – by comparison, the Amazon had 2.6 times more trees, but in an area 6.4 times larger.

The scientists say this expert-vetted checklist for New Guinea should be invaluable for conservation planning in the future. The world’s indicator of species’ status the IUCN Red List of Threatened Species requires accepted plant names and geographic distributions to make their conservation assessments, which includes modelling the impact of changes in climate and land use on plants. This data, which can be used by IUCN, will help to ensure the safety of the island’s flora.

The checklist should also facilitate the discovery and characterisation of even more new species on the island. The current collecting effort is still low, while land use change is an increasing threat to the biodiversity. More botanical exploration is urgently needed so species, as yet unknown to science, can be collected, studied and protected. Since 1970, 2,812 new species have been published from New Guinea and the authors estimate that in 50 years, up to 4,000 species will be added to the list

By making this checklist available globally, the authors hope that efforts will be scaled up to train the next generation of New Guinea plant taxonomists, to digitise and unify historical collections around the world, and to find long-term financial support to accelerate research.