Canada lettuce (Lactuca canadensis)
Canada wild lettuce
Lactuca canadensis L. var. integrifolia (Bigelow) Torr. & A. Gray
Lactuca canadensis L. var. latifolia Kuntze
Lactuca canadensis L. var. longifolia (Michx.) Farw.
Lactuca canadensis L. var. obovata Wiegand
Lactuca canadensis L. var. typica Wiegand
Lactuca sagittifolia Elliott
Lactuca steelei Britton
CONFIRMATION STATUS: Pending confirmation.
TAXONOMY: The currently accepted scientific name for Canada
lettuce is Lactuca canadensis L.
NATIVE STATUS: Native, United States and Canada.
GENERAL BOTANICAL CHARACTERISTICS:
Habit: This biennial plant is an erect, usually unbranched and very stout,
standing 3-8' tall. The central stem is approximately cylindrical and glabr-
ous or rarely coarsely-hairy, light green or reddish green (sometimes with
purple streaks), with a some- what waxy appearance.
Leaves: The alternate leaves are light green to dark green, sometimes with
purple edges or a yellowish cast. They are up to 10" long, 3" across, and
linear-ovate, egg-shaped, or lanceolate-oblong in shape, although there is
a high degree of variability in leaf shape. The largest leaves have deep pin-
nate lobes, while the smaller leaves have shallow pinnate lobes or none.
The leaves are wider at their bases than at their tips, and their bases clasp
directly with the stem. Basal and lower stem leaves sickle-shaped to linear-
ovate or egg-shaped, 6 to 14 inches long, 1.6 to 5.6 inch wide. Occasional-
ly, the leaves have widely spaced small teeth along their margins and short
fine stiff hairs along the underside of their central veins. The leaf surface
can be shiny or dull.
Flowers: The inflorescences structure is a panicle, much-branched, diffuse,
cone-shaped, terminal. The small dandelion-like flowerheads occur in a
narrow panicle up to 2' long at the apex of the plant. There may be 50-100+
heads, cylindric, less than 1/2 inch across, 1/3 to 1/2 inch tall. The petaloid
rays of the florets are yellow or slightly reddish to pinkish orange. The
anthers are yellow and protruding. There is no disk florets. Each flower-
head is about 1/3" (8 mm.) across, consisting of 12-25 ray florets. Around
the base of each flowerhead, there are several floral bracts (phyllaries) in
several series that are appressed together and vary in size. These bracts are
light green and glabrous; sometimes they are tinted purple or red. Bracts
overlap about 1/3 inch long at flowering and 1/2 inch long in fruit, usually
bent downward in fruit. Outer bracts lanceolate, inner bracts linear. There
is no noticeable floral scent.
Fruit/Seeds: The flowers are replaced by dark brown achenes with tufts
of white hair, which are attached together by thread-like beaks. Each
achene has a central longitudinal ridge with some black splotches on
either side. Achenes are ovoid, flattened in shape, and slightly curved, 1/5
to 1/4 inch long (including thread-like beak), 1/12 inch wide. The length
of the achenes is equal to, or greater than, the length of their attached beaks.
The inflorescence often has buds, flowers, and achenes existing together
in different stages of development. The achenes are distributed by the wind.
Roots: The root system consists of a thick deep taproot. There is a white
latex in the root, leaves, and stems.
REGENERATION PROCESS: Canada lettuce propogates itself by re-
HABITAT TYPES: Canada lettuce can be found adjacent to (but rarely
part of) natural, undisturbed habitats, including woodland margins and
clearings, stream and river banks, margins of lakes and ponds, rocky open
woods, thickets, marshes, sandy pine plains, and conifer swamps. It is
much more likely to be found in disturbed areas, including waste places,
roadsides, pastures, borders and trails forests and fields and the fields themselves, and railroads. Canada lettuce is an aggressive early succes-
sional plant that promptly invading disturbed sites and clearings.
SITE CHARACTERISTICS: Canada lettuce prefers full or partial sun,
and moist to slightly dry conditions. Growth is best in fertile loamy soil,
although poor gravelly or rocky soil, sandy, and clay-loam are also tolerat-
ed. This plant varies considerably in size depending on growing conditions.
SEASONAL DEVELOPMENT: The blooming period occurs during late
summer or early fall (July, August, September), lasting about 3-4 weeks.
GENERAL DISTRIBUTION: Canada lettuce is found throughout all
of the states in the United States (except Arizona and Nevada) and all
Canadian provinces (except Saskakatchen) and the far northern provinces.
SKY MEADOWS DISTRIBUTION: To be determined.
IMPORTANCE AND USES: The nectar and pollen of the small flowers
attract bees primarily, such as the leaf-cutting bee Megachile latimanus
and the Halictid bee Lasioglossum lustrans. The caterpillars of some moths
feed on Lactuca spp. These species include Autographa precationis (com-
mon looper moth), Grammia virgo (virgin tiger moth), and Cucullia inter-
media (intermediate cucullia); the caterpillars of the last of these moths feed
on the florets. Several aphid species use Lactuca spp. as host plants; they
include Hyperomyzus lactucae (currant-sowthistle aphid), Nasonovia
ribisnigri (currant-lettuce aphid), Prociphilus erigeronensis (white aster
root aphid), Uroleucon ambrosiae (brown ambrosia aphid), Uroleucon
gravicorne, Uroleucon pseudambrosiae (false ambrosia aphid), Uroleucon
sonchella (sowthistle aphid), and Pemphigus bursarius (lettuce root aphid).
Among vertebrate animals, the eastern goldfinch occasionally eats the seeds.
Notwithstanding the bitter white latex in the foliage, mammalian herbivores
occasionally browse on the foliage of this plant. The cottontail rabbit eats the
tender leaves of first-year plants, while white-tailed deer eats the tops off of
more mature plants. Horses, cattle, and sheep also feed on this plant. When
grazed, the plant can cause milk to be tainted.
Native Americans would steep the roots and bark and take the tea for back
and kidney pains; took a tea to induce sleep; applied a poultice of pulveriz-
ed roots to stop bleeding cuts; and used the milky latex to treat poison ivy
sores. The leaves were cooked and eaten as greens.
Crooked Run Valley