karrikin

thumb|Chemical structures of karrikins (KAR1, KAR2, KAR3, and KAR4) Karrikins are a group of plant growth regulators found in the smoke of burning plant material. Karrikins help stimulate seed germination and plant development because they mimic a signaling hormone known as strigolactone. Strigolactones are hormones that help increase growth of symbiotic arbuscular mycorrhizal fungi in the soil, which enhances plant growth and leads to an increase in plant branching.

Smoke from wildfires or bushfires has been known for a long time to stimulate the germination of seeds. In 2004, the butenolide karrikinolide (KAR1) was shown to be responsible for this effect. Later, several closely related compounds were discovered in smoke, and are collectively known as karrikins.