Wild Lettuce grows as a tall, erect biennial, reaching up to 8 feet high.
Stems are leafy, smooth, light green or reddish green, sometimes have purple streaks, and contain a milky juice and are unbranched until the inflorescence.
Leaves vary considerably, from entire to toothed, to pinnately divided and have a narrow unstalked base or a clasping base. Larger leaves tend to have deep pinnate lobes, smaller upper leaves maybe entire with a sessile base. The leaf edges are not spiny, teeth are widely spaced and the underside of the midrib vein will have fine short hair.
Inflorescence: Flowers appear in a loosely branched panicle that is long and cone shaped and contains many flower heads. It is late flowering and the inflorescence will have buds, flowers and seed heads at the same time.
The flowers, resembling dandelions, are small (under 3/8 inch) with 15 to 20+ yellowish bisexual ray flowers (a few plants have bluish rays but that is the exception); flower heads have involucres campanulate to cylindric in shape, longer than wide. The involucre has small green bracts (calyculi) which reduce in size and grade into the phyllaries which are in several series with the outer ones shorter than the linear inner ones. These reflex when the head is in fruit. The receptacle of the flower is considered 'epaleate' (that is, lacking paleae - which are small bracts that subtend each floret). The filaments and anthers of the five stamens of each ray flower are tightly appressed around the style. Each flower rapidly absorbs moisture and fades away the same day it opens - said to be 'deliquescent'.
Seeds are a brown, oblong-oval, dry cypselae (seeds in composite plants that resemble an achene), with one noticeable nerve line on the side (although they may be up to 3 on some), a long thin beak, and are transported by the wind via a tuft of white bristles (pappus).
Habitat: Wild Lettuce grows from a deep taproot. It tolerates poorer soils but does best in fertile loam and full sun, while some shade is tolerated as are moist to dry conditions.
Names: The genus Lactuca is applied to the lettuce family and comes from the Latin lac, for the milky juice of the stem and root. The species canadensis means 'of Canada', the original type location. The author name for the plant classification - 'L.' refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.
Comparisons: A similar plant is Prickly Lettuce, Lactuca serriola, but there the leaves have prickly edges and spines on the underside of the midrib. Blooming earlier, but still around at the time Wild Lettuce blooms are the Sow Thistles. The flowers of of Spiny Sow Thistle, Sonchus asper, somewhat resemble Wild Lettuce but are slightly wider and the leaves also are prickly. The most similar plant is Tall Blue Lettuce, L. biennis, but there the florets are mostly bluish or cream-colored and the leaves a darker shade.
Below: 1st photo - A flower with 17 rays. Flower are only open part of a day. 2nd photo - The seed head of Wild Lettuce. Note the reflexed phyllaries.
Below: 1st photo - The basal rosette of next years plant. 2nd photo - Detail of the individual cypselae (achenes) with their fluffy white hair attached to a long beak.
Below: 1st photo - An example of the larger leaves, deeply lobed with a narrow sessile base and few, widely spaced teeth. 2nd photo - Detail of the flower involucre. The outer phyllaries have pointed tips and are shorter than the inner. 3rd photo - The inflorescence with flowering mostly over and some seed heads with the fluffy white pappus ready to take to the air.
Below: 1st photo - An upper stem leaf. 2nd photo - The main greenish-red stem. 3rd photo - Prior to flower opening.
Notes: Wild Lettuce is indigenous to the Garden area. It is found in North America in all the Canadian Provinces except the far north and Saskatchewan and in all the lower 48 states except Arizona and Nevada. In Minnesota it is known in all counties in the NE quadrant, most of the SE and NW quadrants, with most exceptions being in the dryer SW quadrant. There are five species of Wild Lettuce in Minnesota including L. canadensis. The other four are: (Tall) Biennial Blue Lettuce, L. biennis; Florida Wild Lettuce [reported as historical only], L. floridana; and Louisiana Lettuce, L. ludoviciana - all those being native - and finally the introduced Prickly Lettuce, L. serriola.
Lore: Densmore (Ref.#5) reports that a use of this plant for warts was common amount the Minnesota Chippewa. She was told "Gather the white liquid which comes out when the stalk is broken and rub this on the wart."
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"