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 rarely yellow.

The bracts (phyllaries) surrounding the base of a flower are variable in size, green often with purple tips, hairless, overlapping, appressed, and the entire structure (involucre) forming a tube ½ to 2/3+ inch (12 to 15+ mm) long. Flower stalks are green and hairless.

Leaves and stems:

Leaves are alternate, rather variable, the lower leaves up to 12 inches (7 to 30 cm) long and 8 inches (3 to 20 cm) wide, deeply lobed and coarsely toothed with sharply pointed teeth. Leaves become smaller and less lobed as they ascend the stem, the upper stem leaves about 4 inches long, 1½ inches wide, mostly unlobed and widest towards the tip. Leaves are stalkless, typically with 2 large, pointed 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 erect, hairless and unbranched except in the flower clusters. Leaves, stems and roots exude a pale orange-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, usually mottled, flattened, 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:

Louisiana Lettuce is an occasional species primarily found in prairies, less often on river banks, railroad rights-of-way, or in open woods. While it may have either blue or yellow flowers (we've never seen yellow ourselves), they are somewhat larger than the other Lactuca species in Minnesota, and only it and Canada Wild Lettuce (Lactuca canadensis) have pale orange-brown sap and flattened oval-elliptic seeds with a beak not longer than the seed body, where the others have milky white sap and different seeds.

As further distinctions, L. canadensis is found in a wider range of habitats, often wooded, and is typically a taller plant, leaves are more deeply lobed, usually has yellow flowers (though may be tinged reddish) with only 15 to 20 rays, and the beak on seeds is more often only about half as long as the seed body. Tall Blue Lettuce (Lactuca biennis) and Woodland Lettuce (L. floridana) both have smaller, blue(ish) flowers, larger seeds with a very short (or absent) stout beak, and leaves lack basal lobes. The non-native Prickly Lettuce (L. serriola) has stiff prickles along the leaf midveins, yellow flowers with only 12 to 20 rays and its seeds are smaller, tapering at the base, with a beak 1 to 2+ times as long as the seed.