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Prickly Lettuce

Prickly Lettuce

Lactuca serriola

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How common: Common

Invasive alien species

Prickly lettuce is a one- or two-year wild lettuce with milky sap and a stiff, upright stem. It favors dry, sunny, disturbed places like roadsides, railways and waste ground. The narrow bluish leaves stand edge-on and tend to line up north–south, and the plant carries many small pale yellow flower heads.

Did you know?

  • Also called a compass plant: the leaves line up roughly north–south.
  • Each small flower head opens for only one day, and usually only in clear weather.

About the species

Identification

Stiff, upright plant 40–100 cm tall with milky sap. Stem pale, mostly smooth, sometimes branched. Leaves narrow to long, bluish grey and hard, usually cut into side lobes with sharp teeth; the base is arrow-shaped and clasps the stem. Leaves stand edge-on and line up roughly north–south, forming two rows. On the underside the main vein has a line of stiff spines. Many slender stalks carry lots of small, pale yellow flower heads about 1–1.5 cm wide; only some open at a time. Later they turn into white, fluffy seed heads. Resembles sow-thistles or dandelions, but those lack the spiny mid-vein and compass-like leaves. Flowers in Finland in July–August.

Plant group

Herbaceous plants

Habitat

yards and roadsides

Flowering

Jul–Aug

About the habitat

Open, sunny, dry and disturbed places such as roadsides, railways, ports, waste ground, urban lots and field margins. Introduced and locally established, mainly in southern urban areas; especially around the Turku region. Found along roadsides, in ports and rail yards, and on waste ground.

Sources

Photo: Tournasol7, CC BY 4.0 https://commons.wikimedia.org/wiki/File:Lactuca serriola in Aveyron (3).jpg

Text: Pinkka: A Pohjolan kasveja - Laburnum-Luzula, CC BY 4.0 https://laji.fi/taxon/MX.39942

Text: FinBIF species descriptions, CC BY 4.0 https://laji.fi/taxon/MX.39942

Text: Wikipedia (Finnish), CC BY-SA 4.0 https://fi.wikipedia.org/wiki/Piikkisalaatti

See also