Kew Gardens plant study reveals more than 2,000 new species
More than 2,000 new plant species were discovered last year, the first study of the global status of plants has found.
The "state of the world's plants" report by the Royal Botanic Gardens, Kew, estimates there are 391,000 vascular plants - which exclude mosses and algae - in the world, with 2,034 new species found in 2015 alone.
New finds include a huge insect-eating sundew discovered via Facebook, five new types of onion, a three-metre (10ft) tall slipper orchid, and a close relative of the sweet potato.
But the report warns that many plants are living on borrowed time in the face of climate change, as they respond only slowly to rising temperatures and changing rainfall and have limited ways they can adapt.
Many plants are already in "extinction debt", it suggests, hit by global warming but with the true impacts not set to be revealed for some time.
Much of the world's land areas are also changing, with increased plant growth or "greening" of the Arctic since 2001 and elsewhere loss of mangroves and forests.
Some 1,771 areas of the world have been identified as "important plant areas" (IPAs), but very few have conservation protection, the study said.
In the UK, which has important habitats such as Atlantic woodlands and Celtic rainforests, 165 IPAs have been identified, from the Lizard Peninsula in Cornwall to the west coast of Scotland, while work is being done to identify sites in UK Overseas Territories.
Globally there are 4,979 invasive plants, with the problem of non-native species such as cheatgrass, spotted knapweed and Japanese knotweed costing £1.7 billion in the UK.
The report also reveals that l ess than a tenth of the world's known plants, around 31,000, are used by humans, with the major uses being medicines, food and fuel.
It highlights the importance of collecting samples of "crop wild relatives", cousins of plants humans use as common crops which may have traits that could help make food plants more resilient to a changing climate or pests and diseases.
There are major gaps in collections of the wild relatives of some key crops, including banana, aubergine and sorghum.
But wild relatives of crops are among some of the plants found last year, such as Canavalia reflexiflora - a legume related to the Brazilian jack bean - five new onions related to the cultivated onion Allium saxatile, and a species of Ipomoea from Bolivia which is a close relative of the sweet potato.
Other new discoveries in 2015 include a 1.5 metre (5ft) tall Brazilian sundew Drosera magnifica, first identified on Facebook by a sundew specialist reviewing photos taken years earlier by an orchid hunter, and a 105-tonne tree Gilbertiodendron maximum, in Gabon.
Professor Kathy Willis, director of Kew Science, said the importance of the study came down to "the role plants play in every aspect of our life," and said the report set a baseline for the first time on key indicators of how plants were faring.
"Given how absolutely fundamental plants are for human wellbeing, for food, fuel, climate regulation, it's pretty important we know what's going on," she said.
Before now, there had been global assessments of the world's birds and mammals but not of plants, she said.
"I do find it extraordinary we worry about the state of the world's birds but we don't worry about the state of the world's plants.
"Unless we look at this information, the knowledge gaps, and then do something about it, we are in a very perilous situation, if we ignore the thing that underpins all our human wellbeing," she warned.