New Guinea has the world's richest island flora

Almost 20 times the size of Switzerland, New Guinea is the world's largest tropical island. It features a complex mosaic of ecosystems ? from lowland jungles to high-elevation grasslands with peaks higher than Mont Blanc. Botanists have long known that this mega-diverse wilderness area is home to a large number of plant species. Efforts to identify and name thousands of plants collected in New Guinea and archived in herbaria all over the world have been ongoing since the 17th century.

However, since researchers have worked mostly independently from each other, a great uncertainty remains as to the exact number of plant species, with conflicting estimates ranging from 9,000 to 25,000. "Compared to other areas like Amazonia, for which plant checklists were recently published, New Guinea remained the 'Last Unknown'," says Rodrigo Cámara-Leret, a postdoctoral researcher in the lab of Prof. Jordi Bascompte in the UZH Department of Evolutionary Biology and Environmental Studies. Under his lead, 99 scientists from 56 institutions and 19 countries have now built the first expert-verified checklist for the 13,634 vascular plant species of New Guinea and its surrounding islands.

Merging databases and human knowledge

The researchers began their large-scale collaborative effort by compiling a list of plant names from online catalogues, institutional repositories and datasets curated by taxonomists. After standardizing the scientific names, 99 experts on New Guinea flora checked almost 25,000 species names derived from over 700,000 individual specimens. For this, they reviewed the list of original names in their plant family of expertise and assessed whether these names were correctly assigned in the online platforms. Finally, an independent comparison was performed between the list accepted by experts and a list contained in Plants of the World Online for New Guinea.

Tremendous, mostly endemic plant diversity

The resulting checklist contains 13,634 plants, demonstrating that New Guinea has the world's richest island flora ? with about 20% more species than Madagascar or Borneo. By far the most species-rich family are the orchids and almost a third of the species are trees. One particularly remarkable finding is that 68% of the plants are endemic ? they are only found in the region. "Such high endemic species richness is unmatched in tropical Asia," says Cámara-Leret, "It means that Indonesia and Papua New Guinea, the two states into which the island is divided, have a unique responsibility for the survival of this irreplaceable biodiversity."

Foundation for research and protection

The new authoritative checklist will improve the accuracy of biogeographic and ecological studies, help focus DNA sequencing on species-rich groups with high endemism, and facilitate the discovery of more species by taxonomists. Thousands of specimens remain unidentified in the collections and many unknown species have yet to be discovered in the wild. "We estimate that in the next 50 years, 3,000 to 4,000 species will be added," says Michael Kessler, co-author of the study and scientific curator of the Botanical Garden of the University of Zurich. These efforts will be important for conservation planning and modelling the impact of changes in climate and land use.

The collaboration also underscores that expert knowledge is still essential in the digital era ? reliance on online platforms alone would have erroneously inflated species counts by one fifth. However, many of the New Guinea plants experts are already or soon to be retired, and almost half of them are non-residents. The researchers therefore advocate building a critical mass of resident plant taxonomists.

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