Strigolactones (SLs) are carotenoid-derived plant compounds that stimulate the germination of root-parasitic weeds. Why a host plant should produce such detrimental signals remained unclear until exuded SLs were shown to also encourage symbioses with arbuscular mycorrhizal fungi. Shortly after this discovery, SLs were found to act internally as endogenous phytohormones to regulate numerous traits, most prominently shoot branching, or “tillering” in cereal crops (Gomez-Roldan et al., 2008; Umehara et al., 2008).