That’s plenty of plants, to be sure, but the total number of plants in the new Kew report surpasses the useful ones by more than a factor of 10: We share the planet with over 391,000 plant species, the Kew scientists say.

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The assessment comes with a big caveat — these species are only vascular plants, or plants that have a specific, specialized tissue for sucking up water through their body. (Plants lacking these ducts, like algae and mosses, weren’t counted.) Of the vascular plants scattered across the planet, 94 percent have flowers.

“It’s really important to know how many plant species there are, where they are and the relationship between the groups, because plants are absolutely fundamental to our well-being,” Kathy Willis, Kew’s science director, told the BBC.

To make their estimate of the planet’s plants, the Kew scientists combed through three previously-existing databases: the Plant List, the International Plant Names Index and the World Checklist of Selected Plant Families. Rather than raking in the names from all three lists, the task laid out before the botanists was closer to taxonomic weeding. Over the years, as various people have identified the same plant at different times or in a different location, plants have accumulated multiple names. Kew determined that each plant in the International Plant Names Index, had 2.7 different species names, on average. By cutting out the duplicates from more than a million different names, the Kew report was able to pare down the known species to a confident 391,000.

With the global report comes a global warning. As many as one in five plants may be at risk of extinction, the scientists say, due to invasive species, disease and changing landscapes. It is tougher to pin down climate change’s potential impacts, given the gradual rate of change and the slow reproductive systems of plants.

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“For most of the major groups of plants we’re talking about, it takes at least 10, 20, 30 years before the next generation starts to produce flowers and pollen,” Willis said to Agence France-Presse. But by 2050, the Kew report notes that species-specific environmental models indicate some plant species, particularly slow-to-react trees, are on “borrowed time.”