For a long time, western science and Indigenous knowledge have been seen as distinct ways of learning about the world. But as we plunge the planet deeper into environmental crises, it is becoming clear that it is time to pay attention to both. Bridging that gap has been the driving force behind the career of the botanist and author of Braiding Sweetgrass, Robin Wall Kimmerer. She tells Madeleine Finlay what we can learn from the most ancient plants on Earth, why we need to cultivate gratitude for the natural world and what western science can learn from Indigenous knowledge