The common name “Chinese Lettuce Weed” most frequently refers to the plant Lactuca serriola, or Prickly Lettuce. This species is the closest wild relative of cultivated garden lettuce (Lactuca sativa), sharing the same genus and characteristics, including the production of a milky sap. Prickly Lettuce is a widespread, non-native annual or biennial plant native to Eurasia and North Africa. It commonly grows in disturbed soils, roadsides, and fields, contributing to its classification as a common weed.
Identifying Prickly Lettuce
Identification of Lactuca serriola is based on several distinct physical features. The plant begins as a basal rosette of leaves close to the ground, but eventually bolts, producing a tall, hollow flowering stem that can reach heights of up to seven feet. The leaves are typically oblong or lance-shaped and are often deeply lobed, with the lower leaves being the largest.
The presence of stiff, spine-like bristles is a key identifier. These prickles are conspicuously aligned along the central vein on the underside of the leaf, and finer prickles line the leaf margins. When injured, the plant exudes a white, sticky latex. Leaves on the mature stem also have ear-like lobes at their base that partially clasp the stem.
The plant earned the alternative name “compass plant” because mature leaves on the main stem often twist and orient themselves vertically along a north-south plane. This vertical orientation minimizes the leaf surface area exposed to the midday sun, serving as an adaptation to conserve water. The plant produces numerous small, pale-yellow flowers, which later develop into fluffy seed heads similar to dandelions, allowing for wide wind dispersal.
Culinary and Historical Uses
The “lettuce” part of the common name acknowledges the plant’s connection to cultivated lettuce. When the plant is very young and still in the rosette stage, its leaves are edible and can be used raw in salads or cooked like other bitter greens, such as dandelion. However, the leaves rapidly accumulate a bitter taste as the plant matures and the flowering stalk begins to elongate.
Historically, the plant’s most significant use was medicinal, rooted in the production of lactucarium. This substance is the milky white sap, or latex, that flows from the stem and leaves when cut. The latex contains sesquiterpene lactones, primarily lactucin and lactucopicrin, noted for their mild sedative and analgesic properties. Due to these effects, it was sometimes historically referred to as “lettuce opium” or “poor man’s opium,” though its effects are significantly milder than those of true opium.
Ancient civilizations, including the Egyptians and Greeks, used wild lettuce preparations to promote sleep and ease various ailments. It was officially listed in the United States Pharmacopoeia in the late 19th century as an ingredient in lozenges, syrups, and tinctures intended to soothe coughs. Contemporary use is generally discouraged because the concentration of active compounds varies significantly depending on the plant’s age, growing conditions, and preparation method. Unregulated quantities can potentially cause negative side effects, including drowsiness or, in rare cases of extreme overdose, restlessness or cardiac issues.
Managing Its Spread
Control efforts must focus on preventing Lactuca serriola from producing seeds. The plant has a deep taproot, which makes removal challenging once it is fully established and mature. The most effective non-chemical control involves manually removing the plant early in its life cycle, ideally when it is still a small basal rosette.
Mechanical removal requires digging or pulling the entire taproot, as leaving the root crown can allow the plant to regrow. If plants are too numerous to pull, cutting the stem off at or below the soil line before any flowers develop will prevent seed production. A single plant can produce tens of thousands of seeds.
Chemical control options are most effective when applied to young plants in the rosette stage. Many selective broadleaf herbicides and non-selective options can control Prickly Lettuce seedlings. Biotypes of Lactuca serriola have developed resistance to certain types of herbicides, including some synthetic auxins and glyphosate. Timing the application before the stem bolts and the leaves become tougher is paramount for maximizing the efficacy of any chemical treatment.