Since fires usually destroy all of the foliage in a given location, the time immediately after a fire is an optimum growing period for seedlings whose access to sunlight would otherwise be blocked by leaves of larger plants. Because of this, some plant seeds have evolved mechanisms for sensing smoke associated with local fires. Grand Rapid lettuce germinates in response to the presence of low concentrations of karrikinolides present in the smoke from burning vegetation.
"Smoke from burning vegetation is recognized as an important environmental cue and promoter of germination for seeds of many species...Previous investigations of smoke-stimulated seed germination demonstrated that dilute solutions of smoke-water were highly effective in promoting the germination of light-sensitive seeds of Lactuca sativa L. cv. Grand Rapids...The major germination compound responsible for the observed germination increase was isolated and identified as 3-methyl-2H-furo[2,3-c]pyran-2-one (karrikinolide), a discovery that has revealed a class of plant bioactive compounds that are referred to as karrikins...[karrikinolide] has been shown to improve germination and improve seedling vigor of several species, including those from fire-prone environments, arable and parasitic weeds, several Australian Solanum species, and crop plants. Due to the fact that it has an effect at extremely low concentrations (as low as 1 nM), it has potential as an important agronomic and horticultural chemical." (Light et al. 2010:267)