Prickly Lettuce, also known as Wild Lettuce or Compass Plant
Kingdom: Plantae, Division: Angiosperms, Class: Eudicots, Order: Asterales, Family: Asteraceae, Genus: Lactuca, Species: L. serriola · Asteraceae (Daisy or Sunflower family) · Simple; deciduous annual or biennial herb
Species
Lactuca serriola
Leaf Type
Simple; deciduous annual or biennial herb
Family
Asteraceae (Daisy or Sunflower family)
Shape
Oblong to lanceolate and deeply pinnately lobed (occasionally unlobed in some variations). The lobes are often backward-pointing.
Size
Typically 2 to 10 inches long and 0.5 to 3 inches wide. The specimen in the image appears to be a mid-sized juvenile, approximately 5-7 inches in length.
Margin
Serrate (toothed) with fine, prickly spines along the edges and a distinctive row of prickles along the underside of the midrib.
Arrangement
Alternate along the stem, often forming a basal rosette in its first year and then spiraling up a central stalk when bolting.
Rarity
Very Common; frequently encountered in urban, suburban, and agricultural landscapes.
Color & Pattern
Pale to medium green with a prominent whitish midvein. The leaves may take on a reddish or purplish tint under stress or as they age. No variegation is present.
Venation Pattern
Pinnate venation with a very thick, light-colored central midrib. The lateral veins are visible but less prominent.
Texture & Surface
The surface is generally smooth (glabrous) but feels stiff and coarse due to the presence of sharp prickles (small spines) along the margins and the underside of the midvein.
Description
Prickly Lettuce is an upright herbaceous plant that can reach heights of 2 to 6 feet. It is characterized by its milky white sap (latex) and its unique ability to orient its leaves vertically in a north-south plane to avoid intense midday sun. It produces small, pale yellow dandelion-like flower heads in late summer, followed by feathery seeds dispersed by wind.
Key Features
The most definitive diagnostic feature is the single row of stiff, sharp prickles along the underside of the leaf's central midrib. The milky sap and vertically oriented 'compass' leaves are also key.
Habitat
Disturbed areas, roadsides, garden edges, vacant lots, and agricultural fields. It thrives in full sun and well-drained, nutrient-rich soils.
Geographic Range
Native to Europe, Asia, and North Africa; widely naturalized across North America, Australia, and other temperate regions where it is often considered a weed.
Condition Notes
The leaves appear healthy and vibrant green with excellent turgidity. Water droplets suggest recent rain or morning dew. No significant insect damage or fungal rust is visible. Grade: Excellent.
Interesting Facts
It is the closest wild relative of common garden lettuce (Lactuca sativa). It is called 'Compass Plant' because the leaves on the upper stem twist at the base to face east and west, with the flat surfaces avoiding the direct south-facing sun to conserve water.
Medicinal & Uses
Historically used in folk medicine as a mild sedative or 'poor man's opium' due to the lactucarium in its milky sap. While young leaves are occasionally eaten as potherbs, they become very bitter and tough quickly. Use caution as the sap can be an irritant.
Ecological Role
While often viewed as an invasive weed, it provides a nectar source for various bees and flies during the summer. Small birds occasionally eat the seeds. Its deep taproot helps break up compacted soil.
Similar Species
Sonchus asper (Prickly Sow Thistle) which lacks the spines on the underside of the midrib; Lactuca virosa (Great Lettuce) which has wider, less lobed leaves and more potent sedative properties.
Foraging Tips
Look for this plant in early spring for edible young shoots before the spines harden and the bitterness increases. Always check the midrib underside to confirm the identity and distinguish it from edible thistles or sow thistles.
Toxicity Warning
Mildly Toxic. The milky latex contains lactucarium, which can cause digestive upset or mild sedation if consumed in large quantities. The prickly spines can cause physical irritation to the skin or mouth. Grade: Mildly Toxic.