By 1850 identifying and classifying plants had become far more important than mere list making. Establishing the global laws of botany - what grew where and why - occupied the well travelled naturalist Joseph Hooker - son of Kew's director William Hooker and close friend of Charles Darwin. Kathy Willis hears from historian Jim Endersby on how Hooker was to acquire species from all over the world to build up the first accurate maps of the world's flora.

Mark Nesbitt, curator of Kew's economic botany collection, reveals how gifts to Hooker in the collection reveal the relationship between the amateur collector in the field and Hooker back at Kew was one built on trust and mutual understanding.

But, as Jim Endersby explains, the relationships were frought with tension when it came to naming new plants. Arguments between those claiming they had found new species (often called "splitters") versus cautious botanists, such as Hooker, who would often "lump" together species as variants of the same, raised new debates about what constitutes a new species. And as Mark Chase, Keeper of Kew's Jodrell Laboratory reveals, the arguments continue today.

Producer: Adrian Washbourne

Presenter: Kathy Willis is director of science at Royal Botanic Gardens at Kew. She is also professor of long-term ecology and a fellow of Merton College, both at Oxford University. Winner of several awards, she has spent over 20 years researching and teaching biodiversity and conservation at Oxford and Cambridge.