Within the cabinets and drawers of the world's herbaria are nearly 400 million dried plant specimens. These collections have long served as a vital record of what plant species exist on Earth and where they grow. But hidden within the desiccated leaves, stems, flowers and roots is far more information on how the plants interacted with their environment while they were alive. Knowing about these "functional traits"—aspects like leaf structure, chemical composition and water content—could help researchers understand how plant communities change over time, and ultimately how we can help ecosystems thrive in the future.