Tall erect plant with small yellow dandelion-like flowers. Leaves have a row of triangular lobes on each side, and spiny teeth all along the edge. Prickly, stalkless, clasping triangular leaf-like bracts under the flowerstalks. The flowers open only in midday sunlight, so are often missed. Fruits like dandelion fluff. Blooms in summer.

Alien weed of waysides and waste places. Occasional in Wildwood, along Wildwood Drive and the Riverway bike path.

The native wild lettuce (L. canadensis) is very similar but has leaves highly variable in shape, often with very deep lobes, but no spiny teeth. Both species are in the same genus as cultivated salad lettuce (L. sativa).