A new study is warning more than a fifth of the world’s plant species are at risk of extinction. The Sampled Red List Index says 22 percent of almost 4,000 species are threatened, with human-induced habitat loss the cause in over 80 percent of the cases. Stephen Hopper of London’s Royal Botanic Gardens said, “We cannot sit back and watch plant species disappear — plants are the basis of all life on Earth, providing clean air, water, food and fuel. All animal and bird life depends on them, and so do we.”