Flower:

Open, branching cluster of stalked flowers at the top of the plant and arising from upper leaf axils. Flowers are ¾ to 1 inch across with 20 to 50 rays (petals) that are pinkish purple to bluish, or sometimes yellow.

The bracts are variable in size, green often with purple tips, hairless, overlapping, appressed, and form a tube ½ to ¾ inch long.

Leaves and stems:

Leaves are rather variable, the lower leaves up to 12 inches long and 8 inches wide, deeply lobed and coarsely toothed with sharp pointed teeth. Leaves become smaller and less lobed as they ascend the stem, the upper stem leaves about 4 inches long, 1½ inches wide, and unlobed. Leaves are stalkless, typically with 2 large lobes (auricles) at the base. Color is green to blue-green.

Leaf surfaces are hairless, but with soft prickles along the edges and the midrib on the underside, sometimes also on major veins. Stems are hairless and unbranched except in the flower clusters. Leaves, stems and roots exude a brown sap when broken.

Fruit:

Flower heads form seed heads about 1½ inches in diameter with the bracts spreading out as seed matures. Seed is dark brown to nearly black, flattened, oval-elliptic, with a slender beak about as long as the seed body, and a tuft of white hairs at the tip of the beak.

Notes:

While Louisiana Lettuce may have either blue or yellow flowers, they are larger than the flowers of either Tall Blue Lettuce (Lactuca biennis), or Wild Lettuce (L. canadensis). L. biennis is further distinguished by the lack of auricles on leaves, winged leaf stalks, and gray-brown hairs on the seeds. L. canadensis is further distinguished by the lack of prickles on leaf edges, having only 15 to 20 rays on the flowers, and usually being a rather taller plant. The non-native Prickly Lettuce (L. serriola) also has prickles along the leaf midveins, but has smaller yellow flowers with only 12 to 20 rays.