While lettuce grows in our garden at its frantic pace, I tend to pick leaves from the core to prevent it from flowering. If not, the leaves don’t grow to size and don’t acquire the same soft texture. But after several cycles, it exhausts itself, and no matter how I pick them, the plant will grow flowering stalks and bloom.
As it bloomed this morning, I was reminded that Lactuca sativa is a member of the daisy family, Compositae aka Asteraceae. Its flowers are like a smaller, yellow version of a chicory’s (Cichoria intybus) reproductive structure. Both are an infloresecence of many tiny flowers known as florets. They each have several 5-toothed petals and the florets consist of five fused anthers that form a tube surrounding the style(female structure that connects the stigma and the ovary).
Although Carl Linnaeus originally thought it was feasible, plants cannot be classified on the basis of flower structure alone. Other structural features are used and in recent decades, botanists have also relied on biochemical and genetic comparisons.
Based on mitochondrial variations, the placement of chicory (Cichorium) and lettuce (Lactuca) in different genera is justified. But chicory and lettuce, as shown from the diagram, are more closely related to each other than to dandelions (Taraxacum) or sow thistles (Sonchus) or Cupid’s dart (Catananche). Lettuce, however, is more closely related to sow thistles (Cicerbita) than to chicory.
Speaking of chicory, in the spring of my youth, my aunts, mother, neighbors and grandmother would comb empty suburban fields for young chicory (and dandelion) leaves and them use them in salads. It’s probably not a coincidence, given the ethnic origin of my relatives and neighbors, that lettuce originated in the Mediterranean area where it too was picked and eaten as a weed. Eventually, ancient Greeks and Romans cultivated lettuce, but were preceded by Egyptians who depicted lettuce on tomb paintings. However, from looking at their artworks, I have a hard time identifying it as lettuce. More certain is that much later, by 1885, the New York Agricultural Experiment Station was growing 83 distinct varieties of lettuce.
Most commercial lettuce on the North American continent is grown in California and Arizona. In the former location there have been some serious E. coli outbreaks in 2018 and 2020. Fields where the plants were grown were close to large feedlots, which the FDA reported could have contaminated romaine lettuce with E. Coli from both dust and contaminated irrigation water from open trenches. Subsequently, there has been closer monitoring by government officials and researchers teams.
What is promising is that lettuce is being increasingly grown on rooftops and in city or home gardens, which reduces the carbon footprint from transporting lettuce thousands of miles from the western parts of the continent to the densely populated eastern parts. And it’s a lot more fun to pick it from one’s backyard than to go buy it at the grocery store.