Figure 1. Karrikin (KAR₁) and active strigolactone analogs. Natural SLs have a four-ring structure exemplified here by the artificial SL GR24. The D-ring (butenolide moiety) is essential for activity of all SL analogs. Small numbers identify atoms mentioned in the text. Compounds 1 and 2 were originally described by Mwakaboko and Zwanenburg²⁴ and Fukai et al.²³ respectively.