Lettuces are annual, biennial, or perennial, leafy-stemmed herbs with milky juice, alternate, entire to pinnately lobed leaves, and usually numerous relatively few-flowered heads (mostly with 13-56 flowers in our species) in a mostly somewhat compound flower cluster. The flowerheads are with all rays and have both stamens and pistils, colored yellow, blue, or white, the corolla tube generally being more than half as long as the ray itself. The involucre is cylindric, often broadening at the base in fruit, having extra bracts or more often with the bracts partly overlapping. The receptacle is naked. The achenes are flattened, winged or strongly nerved marginally, with 1 to several lesser nerves on each face, beaked or beakless, but in any case expanded at the summit where the pappus is attached. The pappus consists of numerous hair-like bristles, none markedly larger than the others, and at least some of them being no more than 4-celled in cross-section at the base. The genus consists of about 50 species worldwide, native to Eurasia, Africa, and N. America. The common cultivated lettuce, L. saliva, which may occasionally escape or persist after cultivation, may be distinguished from any of the following by its very broad, merely toothed leaves. The name comes from the ancient Latin name, from lac, milk, referring to the milky juice of the plants.
Guide to Identify Presented Species of Genus Lactuca
L. tatarica Blue Lettuce Hairless plant, 20-100 cm tall. Meadows, thickets, plains to foothills.
Flowerheads blue, about 2 cm wide, with 18-50 rays, in open clusters.
Leaves alternate, narrowly lance-shaped, entire, the lower leaves with lobes.
L. serriola Prickly Lettuce Stem 30-150 cm tall, hairless, branching at sharp angles. Weed, disturbed areas.
Flowerheads 10-15 mm wide, with 13 to 27 ray florets, in open clusters.
Leaves alternate, pinnately lobed, prickly on the midrib beneath and on edges.