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Prickly Lettuce (Lactuca serriola)

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Summary

Prickly lettuce is a widely-distributed plant, native to Europe, Asia, and North Africa, and introduced to North America where it is widely considered weedy and invasive.

USDA Plants Profile for Lactuca serriola

Illinois Wildflowers Page for Lactuca serriola

Description & Identification

Highly variable in height; can grow tup 7' but usually much shorter. Leaves are alternate and clasping the stem at the base, variably lobed, ranging from unlobed to deeply cut with many lobes. Leaf margins are prickly, and prickles also run along the central vein. Unlike thistles, prickles are not usually stiff enough to puncture skin. Leaves and stem both emit a milky white sap when cut.

Has a taproot.

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Habitat

Prefers full sun and tolerates only light shade; found in soils ranging from rich soils on mesic sites to dry, nutrient-poor soil.

In most of eastern North America, found only on disturbed ground in anthropogenic habitats, including roadsides and railroads, gardens, abandoned fields, and waste ground. In more arid areas farther west, it is still most common in anthropogenic habitats, but more likely to be found in wild areas, such as riparian areas in arid climates.

Life Cycle

Prickly lettuce is an annual or biennial, in the sense that it sometimes blooms during the same year it germinates, but sometimes grows only as a basal rosette of leaves during the first year. Which happens depends both on timing of seed germination, and conditions.

Plants establish a taproot upon sprouting. Basal rosettes grow flat to the ground in winter; in spring, they take on a more rounded, bushy growth habit, and they begin to bolt upward late spring to early summer.

Usually blooms mid-summer, sometimes later.

Produces wind-dispersed seeds; plants die after setting seed.

This plant usually depends on disturbance to remain present in an area.

Uses

This species has sometimes used for producing Lettuce Opium or Lactucarium, a sedative milder than opiates, although the closely-related Lactuca virosa is more often used for this purpose.

Lactuca serriola is closely related to cultivated lettuce (Lactuca sativa), and can hybridize with it.

There are also numerous Lactuca species native to North America, as well as other introduced species; L. serriola is the most abundant introduced lettuce in most of North America. In terms of its ecological niche, it is probably most similar to L. canadensis, which grows taller and is slightly more shade-tolerant.

Notes

This plant has evolved resistance to several herbicides.

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