Which tree is often used in the treatment of cancer? Which everyday condiment is the most widely traded spice on the planet? Plants are an indispensable part of our everyday lives. From the coffee bush and grass for cattle (which give us milk for our cappuccinos), to the rubber tree that produces tyres for our cars, our lives are inextricably linked to the world of plants. The Curator of the Oxford University Herbaria identifies the plants that have been key to the development of the western world.