Lactuca canadensis

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Lactuca canadensis
Lactuca canadensis IWF.jpg
Photo by the Illinois Wildflowers Database
Scientific classification
Kingdom: Plantae
Division: Magnoliophyta - Flowering plants
Class: Magnoliopsida - Dicots
Order: Asterales
Family: Asteraceae
Genus: Lactuca
Species: L. canadensis
Binomial name
Lactuca canadensis
Natural range of Lactuca canadensis from USDA NRCS Plants Database.

Common Name: American wild lettuce;[1] Canada lettuce[2]

Taxonomic Notes

Synonym: L. sagittifolia; L. steelei[2]; L. canadensis var. latifolia Kuntze; L. canadensis var. longifolia (Michaux) Farwell; L. canadensis var. obovata Wiegand


Lactuca canadensis is a dioecious annual and biennial that grows as a forb/herb.[2] Its inflorescence consist of a cluster of small pale yellow flowers. When crushed, its foliage excretes a milky juice. Leaves are alternate, simple, with lobed margins.[3] Leaf shape changes with available water and sunlight. Growth in Denver swamps produced larger leaves while plants in direct sunlight were more lobed than the non-lobed plants grown in shade.[4] In Nebraska, it reaches 61 in (1.55 m) in height and 27 in (0.69 m) wide on the surface.[3] Roots are tender and milky spreading out 35 in (0.90 m) and reaching 26 in (0.66 m) deep.[5]


This species occurs in all of the lower 48 United States excluding Nevada and Arizona. In Canada, it is found in all the provinces except Saskatchewan, Nunavut, and Northwest Territories.[2]



L. canadensis is found in fields, roadsides, disturbed ground,[1] thickets, forest edges, and in forest clearings (as cited in [6])


In the southeastern and mid-Atlantic United States, this species flowers from June through November.[1] Flowers on the Florida panhandle have been reported in May, June, and August, peaking in June.[7]

Seed dispersal

This species is thought to be dispersed by wind. [8]

Seed bank and germination

Tennessee topsoil produced 2,683 individuals ha-1 (26.83 individuals Dm-2).[9]

Use by animals

In Minnesota, browsing by white-tailed deer (Odocoileus virginianus) reduced the height (63.8 cm with browsing versus 136.9 cm without). Also, flowering was over 7 times greater on unbrowsed (231 flower heads per plant with browsing versus 1,725 without) L. canadensis plants.[10] Seeds from L. canadensis also provide a resource for wintering birds such as tree sparrows (Spizella arborea). In Illinois, seed traps found densities of 72 g seeds hm-2 during winter months.[11]

Conservation and Management

Cultivation and restoration

Photo Gallery

References and notes

  1. 1.0 1.1 1.2 Weakley AS (2015) Flora of the Southern and Mid-Atlantic States. Chapel Hill, NC: University of North Carolina Herbarium.
  2. 2.0 2.1 2.2 2.3 USDA NRCS (2016) The PLANTS Database (, 30 January 2018). National Plant Data Team, Greensboro, NC 27401-4901 USA.
  3. 3.0 3.1 Plant database: Lactuca canadensis. (30 January 2018) Lady Bird Johnson Wildflower Center. URL:
  4. Talbert CM, Holch AE (1957) A study of the lobing of sun and shade leaves. Ecology 38(4):655-658.
  5. Cole HE, Holch AE (1941) The root habits of certain weeds of southeastern Nebraska. Ecology 22(2):141-147.
  6. Lebeda A, Dolezalova I, Ferakova V, Astley D (2004) Geographical distribution of wild Lactuca species (Asteraceae, Lactuceae). Botanical Review 70(3):328-356.
  7. Nelson, G. PanFlora: Plant data for the eastern United States with emphasis on the Southeastern Coastal Plains, Florida, and the Florida Panhandle. Accessed: 30 JAN 2018/
  8. Kirkman, L. Katherine. Unpublished database of seed dispersal mode of plants found in Coastal Plain longleaf pine-grasslands of the Jones Ecological Research Center, Georgia.
  9. Farmer RE Jr, Cunningham M, Barnhill MA (1982) First-year development of plant communities originating from forest topsoils placed on southern Appalachian minesoils. Journal of Applied Ecology 19(1):283-294.
  10. Shelton AL, Inouye RS (1995) Effect of browsing by deer on the growth and reproductive success of Lactuca canadensis (Asteraceae). The American Midland Naturalist 134(2):332-339.
  11. West GC (1967) Nutrition of tree sparrows during winter in central Illinois. Ecology 48(1):58-67.