Prickly Lettuce

Composite or aster (Asteraceae family):

Lactuca serriola L.

EPPO code:

LACSE

Other names:

Wild lettuce, compass plant

Species information

Lifecycle:

Winter annual, annual or biennial.

Propagation:

Reproduces by seed.

Emergence:

The majority of seeds will germinate in autumn with seedling plants often in the rosette stage in the spring.

Habitat:

Prevalent throughout the province in waste areas, pastures and roadsides and in agricultural crops under minimum till or no-till cropping systems.

Competitiveness:

Ontario studies have shown yield losses as high as 80% when no-till soybean was competing with prickly lettuce at a density of 50 plants/m² while no yield losses in winter wheat were observed even though prickly lettuce densities were as high as 200 plants/m² (Weaver et al., 2006).

Identification clues

Seedling

Cotyledons:

Rounded and tapering to the base.

First leaves:

A basal rosette with club-shaped leaves having finely-toothed margins.

Mature leaves:

Alternate orientation on the stem, variable in size and shape ranging from deeply lobed to without lobes but having spiny toothed margins and a prominent single row of stiff, sharp prickles on the midrib of the leaf’s underside; exudes a milky white juice (latex) when broken.

Mature plant

Stems:

Erect, hollow and hairless; ranging from 30-150 cm tall; green to reddish-green; exudes latex when broken.

Flowers:

Flower heads are made of yellow ray florets and are 8 to 10 mm in diameter; the flower heads are borne at the end of long fine stalks and arranged in a pyramidal panicle.

Seeds:

Yellowish-brown to brown, 2–4 mm long with prominent ribs on each side and attached to a white feathery pappus that most refer to as “fluff”.

Roots:

Fleshy taproot.

Often mistaken for

I know it's not Annual or perennial sow-thistle because prickly lettuce’s mature leaves have a row of spines on the underside of its leaf midrib.