Mark tells Jim Al-Khalili how he came to be a forensic botanist. After working in bars and clubs in Soho for many years, he decided to study for a degree in botany and developed a special interest in water moulds. As a curator of the botanical collections at the Natural History Museum in London, he became intimately acquainted with British flora past and present. And, more recently, has spent a lot of time monitoring urban wildlife – recording how the composition of native species and non-native species in the capital is changing, as the global climate changes and the global trade in plants continues.

Producer: Anna Buckley