Medicines for HIV and cancer could be lost because plants used in their preparation are facing extinction, experts have warned. Deforestation and over-collection now threaten the survival of up to 400 key plant species, according to a survey by the Botanic Gardens Conservation International (BGCI). The at-risk plants include yew trees whose bark is used in cancer drug Paclitaxel and autumn crocus, below, which helps to fight leukaemia.

'Medicinal plants harvested from the wild remain of immense importance for the wellbeing of millions of people around the world,' said BGCI secretary general Sara Oldfield.

More than 50 per cent of drugs prescribed by doctors are derived from chemicals first identified in plants.