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Canada lettuce gets up to 8' tall (and is quite impressive when it does), but is usually considerably shorter. On larger plants, the inflorescence is an apical pyramid 2' tall covered with dandelion-like flowerheads; on smaller plants the flowerheads may be more scattered. Flowerheads are yellow or "dirty orange," a bit over 1/4" wide with a 1/2" long calyx and 15-22 ray florets with toothed tips, each with five stamens and a bifurcated style; there are no disc florets. Seeds are oval, flattened, and attached to a tuft of threads (like a dandelion). Small Canada lettuce plants are superficially similar to prickly lettuce (Latuca serriola), but the latter has large spines on the underside of the main veins of the leaves and seeds that are attached to the tuft of hairs by a beak twice as long as the seed.

Lactuca

Lactuca canadensis

Canada lettuce [Blooms: Jul-Sep]

Prickly lettuce flowerheads dandelion-like, a distinctive pale lemon-yellow color, and 1/4-1/2" across; there are about 20 ray florets with squared, serrated ends (with five teeth), five stamens with yellow anthers, and a bifurcated style whose base is surrounded by the anthers. The seeds are attached to the tuft of hairs by a beak up to twice as long as the seed. Prickly lettuce is superficially similar to Canada lettuce (Latuca canadensis), but the latter has no spines on the leaves and seeds that are attached to a tuft of hairs by a beak no longer than the seed. Prickly lettuce is the closest wild relative to domestic lettuce (L. sativa).

Lactuca

Lactuca serriola

prickly lettuce [Blooms: Jul-Sep]