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Lactuca serriola

prickly lettuce

Europe, western Asia, northern Africa; naturalized across all 50 U.S. states, all Canadian provinces, and temperate regions globally

Deer Resistant Drought Tolerant

SunFull Sun

WaterLow · drought-tolerant

Overview

Lactuca serriola is a tall stiff winter annual or biennial weed in the daisy family (Asteraceae) reaching 24–72 inches (60–180 cm) tall and 12–24 inches (30–60 cm) wide. The species is the wild ancestor of cultivated lettuce (L. sativa) and remains a significant crop wild relative for modern lettuce breeding programs. Stems are erect, stiff, branching in the upper half, pale green, with scattered prickles along the lower stem, exuding copious milky white latex when broken. Basal leaves are oblong, 4–12 inches (10–30 cm) long, irregularly lobed to pinnatifid, with a row of stiff sharp prickles along the underside of the midrib — the principal tactile identification character, visible to the eye and felt as backward-pointing barbs when a finger is run from the tip toward the leaf base. Upper stem leaves run smaller, often unlobed, clasping the stem with pointed auricles (ear-like basal projections). In full sun, leaves orient vertically in a north-south plane, minimizing midday sun exposure — the 'compass plant' habit carried in the common name. Flower heads are small, 0.3–0.4 inch (8–10 mm) across, with 12–20 pale yellow ligulate florets, borne in large open panicles. Fruit is a flattened ribbed achene with a slender beak and white pappus. A single plant produces 2,000–10,000 seeds. Seeds germinate primarily in fall, with rosettes overwintering through the following spring. A widespread urban and agricultural weed across all temperate regions of the globe. Not known to be toxic to pets or humans.

Native Range

Lactuca serriola is native to Europe, western Asia, and northern Africa, occurring in roadsides, waste ground, cultivated fields, and urban areas from sea level to approximately 6,500 feet (2,000 m) elevation. The species is established globally as a cosmopolitan weed — present in all 50 U.S. states, all Canadian provinces, and temperate regions across South America, Australia, New Zealand, and much of Asia.

Suggested Uses

Used in weed identification courses for teaching the yellow-flowered Asteraceae complex (Lactuca spp., Sonchus spp., Crepis spp., Hypochaeris spp., Taraxacum spp.) — the prickly midrib is the primary tactile identification exercise separating Lactuca serriola from its close relatives. The compass-plant leaf orientation in full-sun positions is taught in plant ecophysiology courses on leaf-angle optimization and midday heat avoidance. The evolutionary relationship to cultivated lettuce (L. sativa) is taught in crop wild relatives and plant domestication coursework, where L. serriola supplies disease-resistance genes to modern lettuce breeding programs through interspecific hybridization.

How to Identify

Habit is erect stiff biennial-to-winter-annual at 24–72 inches (60–180 cm) tall and 12–24 inches (30–60 cm) wide. Stems are pale green with scattered prickles below and copious milky white latex exuding from breaks. Basal leaves are oblong 4–12 inches (10–30 cm) long, irregularly lobed to pinnatifid, with a row of stiff sharp prickles along the underside of the midrib — the primary identification character. Upper stem leaves are smaller, often unlobed, clasping with pointed auricles. Flower heads are small (0.3–0.4 inch / 8–10 mm across) with 12–20 pale yellow ligulate florets in large open panicles. The compass-plant leaf orientation (north-south vertical plane) in full-sun positions separates this species from many other yellow-flowered Asteraceae. Compared with Sonchus spp. species (sow-thistles), the midrib is prickly rather than smooth, achenes are flattened and beaked rather than cylindrical and unbeaked, and clasping leaves have pointed rather than rounded auricles; compared with Mycelis muralis (wall lettuce), overall size runs 1–4 feet rather than 0.5–2 feet and flower heads carry 12–20 florets rather than exactly 5; compared with Lactuca sativa (cultivated lettuce), leaves are prickly along the midrib rather than smooth and the plant bolts into tall flowering stems rather than remaining a dense basal rosette.

Appearance

Size & Dimensions

Height2' - 6'

Width/Spread1' - 2'

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~8 weeks

Summer Fall

Small flower heads 0.3–0.4 inch (8–10 mm) across with 12–20 pale yellow ligulate florets appear in large open panicles from June through September in temperate zones. Individual flower heads open for one morning and close by afternoon — a behavior shared across yellow-flowered Asteraceae. The large open panicle produces heads sequentially over a 6–8 week bloom window. The species is self-pollinating. Seeds mature 2 weeks after flowering and disperse by wind via the white pappus. In the Pacific Northwest, peak flowering runs July through August.

Detailed Descriptions

Flower Description

Pale yellow; small flower heads 0.3-0.4 inch across with 12-20 ligulate florets in large open panicles; June-September

Foliage Description

Blue-green; oblong 4-12 inches long, irregularly lobed to pinnatifid, with a row of stiff sharp prickles along the underside of the midrib; upper stem leaves smaller, often unlobed, clasping with pointed auricles

Growing Conditions

Sun Requirements

SunFull Sun

Requires 6-12 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.5 - 8.5(Neutral)

357912

Soil Types

loam sand silt clay rocky

Drainagewell drained

Water & Climate

Water Needs

Low

Frost Tolerance

hardy

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Management by hand-pulling or hoeing before bolting works well, as the fleshy taproot extracts from moist soil with moderate effort at the rosette stage before stem elongation. Once bolted into the tall flowering phase, the stiff stem is hard to pull without a digging tool and plants typically require cutting at ground level instead. Cutting at ground level before seed set prevents reproduction since the taproot does not resprout reliably after severance below the root crown. Mowing at the rosette stage in late winter through early spring prevents bolting into the reproductive phase. The midrib prickles make handling uncomfortable without gloves. Dense mulching with 2–3 inches (5–8 cm) of organic material suppresses the fall germination flush through light exclusion. In agricultural settings, prickly lettuce is a widespread weed in no-till and reduced-tillage systems where fall-germinating seedlings establish under winter cover crops and bolt in spring ahead of the cash crop.

Pruning

No horticultural pruning applies. Plants are removed by pulling, hoeing, or cutting at ground level before seed set. The annual or biennial life cycle means plants do not persist from roots after complete severance below the root crown. Removing the large flowering panicle before seed maturity prevents the substantial seed rain (2,000–10,000 seeds per plant) from a single mature specimen.