The algal morphogen (−)-thallusin was stereoselectively synthesized by implementing an Ir^I-catalyzed enantioselective polyene cyclization. A TMS group tracelessly directed the regioselectivity. (−)-Thallusin is secreted by bacteria associated with the green seaweed Ulva and forms a stable 2:1 Fe^III complex that the algae take up, selectively promoting their massive development. More information can be found in the Research Article by T. Wichard. H.-D. Arndt and co-workers (DOI: 10.1002/chem.202304007). Background picture: Seaphotoart/Alamy Stock Foto.