Monday, July 25, 2016

Meatless Monday: The Ubiquitous Prickly Lettuce

Even in the midst of this year’s rainfall deficit in Connecticut  [currently down about 6 inches from its usual total], the wild urban plants continue to thrive. One of the most prolific inhabitants of the space between fence and sidewalk is prickly lettuce (Lactusa serriola), so named for the prickly spines on the underside of its leaves. An ancestor to today’s salad lettuces, Lactusa serriola is a member of the sunflower family and is native to Europe. 

Prickly lettuce has a basal rosette of pale green leaves from which rises a single hollow stem that can grow to 7 feet! Its alternate leaves are deeply lobed; they typically orient themselves vertically toward the sun, rather than horizontally, leading to the nickname “compass plant.” The tops of the leaves are smooth, but the bottom is prickly, particularly along the midrib [an easy way to distinguish this plant from the dandelion whose leaves have a somewhat similar appearance]. It has a long and sturdy taproot and spreads by re-seeding. Like its modern-day relatives, prickly lettuce grows best in nutrient-rich soils, but it can tolerate dry sites with poor soil, one of the reasons it thrives when lawns are turning brown!

Tiny flowers, gone by.

Pods starting to form.
Prickly lettuce was traditionally used in herbal medicine as a sedative and a painkiller, hence one more nickname, “opium lettuce.” Some modern day foragers gather and eat its shoots or smoke its leaves, but most authorities caution against harvesting and using this plant as it is known to have toxic effects. In fact, WebMD has listed a number of warnings to those who decide to experiment with this plant. They urge everyone to avoid eating wild lettuce in large quantities, but the site also lists a number of immediate dangers to ingesting even a small amount of this plant for those with medical conditions including enlarged prostate, an allergy to ragweed, or narrow-angle glaucoma, as well as for those taking prescribed sedatives or about to have surgery. As a food source, perhaps it is best to leave this lettuce alone.

The plant is particularly troublesome to wheat farmers because the buds can be difficult to screen out of grain. The latex can clog equipment. However, rather than demonizing the wild lettuce, Washington State researchers chose to explore its possibilities as a cash crop. They were intrigued by the milky sap the plant exudes from all its parts when it is broken. A 2006 study had found that the latex in prickly lettuce was very similar to the polymers in natural rubber. The WSU researchers began by mapping prickly lettuce DNA. The initial findings were published in 2015 and seem promising; regions in the plant’s genetic code were found to be similar to those of plants used in the production of rubber. This is indeed good news as the Brazilian rubber tree, our main source of natural latex, is threatened by disease; over half of our rubber products are now being made from petrochemicals. Perhaps one day prickly lettuce will be cultivated and our tires will be made from this wild plant.

Prickly lettuce has one other property I should mention. Peter Del Tredici, author of Wild Urban Plants of the Northeast, states that this plant can be used in phytoremediation of urban sites contaminated by heavy metals, particularly zinc and cadmium. [Another reason not to eat prickly lettuce harvested from a parking lot.] 

I hope you have enjoyed this tale of a plant that you most likely have seen but may not have noticed. If so, you might also like to read my past posts on the wild carrot and purslane

Happy Monday!

I often blog on food, food issues, or topics related to growing things on Monday in support of Meatless Monday, one of several programs developed in the Healthy Monday project, founded in 2003 in association with Columbia University’s Mailman School of Public Health, Johns Hopkins Bloomberg School of Public Health and Syracuse University’s Newhouse School of Communications. Meatless Monday’s goal is “to help reduce meat consumption 15% in order to improve personal health and the health of our planet.”