Tropical rainforests exhibit high levels of biodiversity. Around 40% to 75% of all biotic species are indigenous to the rainforests.[6] Rainforests are home to half of all the living animal and plant species on the planet.[7] Two-thirds of all flowering plants can be found in rainforests.[3] A single hectare of rainforest may contain 42,000 different species of insect, up to 807 trees of 313 species and 1,500 species of higher plants.[5] Tropical rainforests have been called the "world's largest pharmacy", because over one quarter of natural medicines have been discovered within them.[8][9] It is likely that there may be many millions of species of plants, insects and microorganisms still undiscovered in tropical rainforests.