They’re slimy and slippery. They’re part of the green film you see on garden ponds. They can clump together and wash up on the shores of beautiful beaches. A lot of them are invisible to the naked eye. These underappreciated organisms called algae are indispensable to the presence of life on earth but not all is straightforward about them. They can be single celled or multi cellular. They can be ugly and slimy or sometimes beautiful: indeed are even a tourist attraction. They may be found in the sea or on land. They can be life-creating and yet life-destroying and toxic in excess. So perhaps it’s time we paid more attention to algae and their evolution. Rajan Datar is joined by Ruth Kassinger, author of Slime: How algae created us, plague us and just might save us; Dr Brenda Soler-Figueroa, a marine scientist at the Smithsonian Environmental Research Centre; Dr Gothamie Weerakoon Senior Curator of Lichens and Slime Moulds at the Natural History Museum of London and author of Fascinating Lichens of Sri Lanka; and Stefan Bengtson, emeritus professor at the Swedish Museum of Natural History.

(Photo: Volvox algae colonies, spherical forms outlined by biflagellate cells interconnected by cytoplasmic bridges. Credit: DeAgostini/Getty Images)