New Guinea, an island located in the Pacific Ocean measuring around 787,000 square kilometers, is the island with the greatest plant diversity in the world. It’s home to more than 13,500 species of plants, two-thirds of which are endemic, according to a new comprehensive study.

The island has fascinated naturalists for centuries. It is home to the best-preserved ecosystems on the planet and to several ecological gradients (transitions between different types of ecosystems), from mangroves to tropical alpine grassland. Nevertheless, there has been no attempt so far to critically catalog the entire vascular plant diversity of the island.

A group of more than 90 botanists from 56 institutions in 19 countries worked with a wide array of samples, the earliest collected by European travelers in the 1700s. They found that the island has 13,634 species from 1,742 genera and 264 families, with New Guinea surpassing plant diversity from other islands on Earth.

“New Guinea is extraordinary: it is a paradise island teeming with life,” said the paper’s lead author, Rodrigo Cámara-Leret in a statement. “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 recognized as a center of biological diversity.”

Only five families represent more than a third of the plant species on the island. The most diverse are orchids, with 2,856 species or 21% of the island species. New Guinea also has 3,962 species of trees, which is four times the number found across all of North America, for example.

A diverse island

Divided into the Indonesian provinces of Papua and West Papua, and the independent state of Papua New Guinea, the island is the most mountainous and largest tropical island in the world. This allows for different habitats, such as mangroves, swamp forests, and montane forests to coexist in close proximity.

The island is located between Malaysia, Australia, and the Pacific. It has a diverse but young geological history, with a large number of species forming in the last million years. Many of the plants are exclusive to the island. For example, 95% of the ginger species and 96% of the African violets here are endemic.

Researchers had long suspected that the island would be very diverse, but data remained very limited. New Guinea had never been systematically surveyed, with previous estimates suggesting that the island could have anything between 9,000 to 25,000 species.

“I was just pleased that we could nail a number. This is not the end, this is a first step,” said Cámara-Leret, who is now trying to encourage researchers from around the world to continue working on this dataset, which will be very important for the International Union for Conservation of Nature (IUCN) Red List assessments.

But the island might be running out of time. Since 2002, it has lost over one million hectares of primary forest and almost two million hectares of total tree cover. More than 50% of the tree cover loss was recorded in Papua New Guinea. The main threats are small-scale agriculture and logging.

The study was published in the journal Nature.