A fifth of the world’s plant species are at risk of extinction, British researchers warned Tuesday in an unprecedented global census of the plant kingdom. The survey by Britain’s Royal Botanic Gardens at Kew, London, said 21 percent of species are under threat. The report, the first of its kind, is intended to become a global reference point for the study of plants.

The study, which estimates there are a total of 390,900 plants known to science, found farming to be the biggest extinction threat, representing 31 percent of the total risk to plants. Logging and the gathering of plants followed at 21.3 percent, with construction work attributing for 12.8 percent of the risk. READ MORE