Tall Blue Lettuce grows as a tall, erect annual or biennial, reaching up to 12 feet high but usually around 7 feet. Stems are leafy, ridged, light green or reddish green, sometimes have purple streaks, and contain a milky juice and are unbranched until the floral array. There can be sparse whitish hair.
Leaves vary considerably. The larger lower leaves tend to have deep pinnate lobes with coarse teeth on the lobes. The lowest have winged stalks, the mid-stem leaves touch the stem without a stalk. The smaller upper leaves are similar in shape and have two small lobes which partially clasp the stem. Most leaves are on the lower 2/3rds of the stem. The upper surface is a dark green and the lower surface is paler in color and the veins on the underside have whitish hairs.
The floral array is a number of long, narrow panicle arrays of small flowers formed on many side branches off the main stem.
The flowers are only 3/8 inch wide but have 20 to 30 small bisexual ray florets with light bluish, usually, or cream colored corollas (seldom yellowish). Only two species of Lactuca have florets that are usually bluish. The 5 stamen filaments and their anthers are appressed to the pistil and the style has a divided tip. Flower heads have involucres campanulate to cylindric in shape, longer than wide. The outside of the head has a grouping of tightly appressed phyllaries with dark tips. These are usually reflexed with the seeds are visible.
The seed is mottled brown, flattened, ellipsoid shaped dry cypselae (seeds in composite plants that resemble an achene), with 4 to 6 nerve lines on the sides and a tawny-brown fluffy pappus attached for wind distribution.
Habitat: Tall Blue Lettuce grows in moist woods and thickets making due with partial sun. Even though this is a short lived plant, it develops a stout taproot.
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, biennis, refers to the plant being biennial (usually). The author names for the plant classification are first - ‘Moench’ is for Conrad Moench, (1744-1805), German botanist, Professor of Botany at Marburg, author of Methodus Plantas hirti botanici et agri Marburgensis, and who named the genus Echinacea. His work was amended by ‘Fernald’ which refers to Merritt Lyndon Fernald (1873-1950) American botanist, Harvard Professor, scholar of taxonomy, author of over 850 papers, editor of the 7th & 8th editions of Gray’s Manual of Botany. In older literature this species was classified as Lactuca spicata.
Comparisons: Similar in height and shape is the Wild Lettuce, L. canadensis. But there the florets are yellow in the majority of plants, the leaves are paler in color with finer teeth on the lobes. The only other species of Lactuca that typically has light blue ray flowers is Lactuca floridana, Florida Wild Lettuce, which a one time was also found in Minnesota but he DNR now lists it as historical. That species is less tall and has fewer ray flowers.
Above: Flowers occur on a number on narrow arrays branching from the main stem. Drawing courtesy USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York.
Below: The corollas of the florets are usually light bluish, some could be cream-color. The phyllaries on the outside of the head have dark purple tips.
Above: A large mid-stem leaf.
Below: The mid-stem is densely covered while the flowering panicle takes up the upper 1/3rd of the stem. Stems can have sparse whitish hair and be green to green with reddish tones to reddish in color.
Below: When in fruit the phyllaries of the flower head reflex backward. Each seed has a tawny pappus for wind distribution. The underside of the leaves have hair on the veins.
Below: Seeds are a mottled brown flattened ellipsoid cypsela with ribbed sides.
Eloise Butler first noted Tall Blue Lettuce in the Garden on Aug. 15, 1915 when she noticed a plant blooming. In her day it was classified as L. spicata. It was still in the Garden at the time of Martha Crone's 1951 census. Tall Blue Lettuce is found throughout North America, except the Gulf Coast states, Arizona and Nevada in the U.S., and is found in all the lower Canadian Provinces. In Minnesota it is found in about one half of our counties, most of the metro area, most of the counties bordering Wisconsin and across the northern part of the state, and then in scattered counties here and there.
There are five species of Wild Lettuce in Minnesota including L. biennis. The other four are: Canada Wild Lettuce, L. canadensis; Florida Wild Lettuce [reported as historical only], L. floridana; and Louisiana Lettuce, L. ludoviciana and the only non-native species, Prickly Lettuce, L. serriola.
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"