Lactuca is a genus of annual or biennial herbs with milky sap, from a taproot and generally forming a leafy rosette the first year.
Leaves alternate, otherwise very various
Flowers yellow, white or blue, in heads of 5-56 florets (in ours), all rays (ligulate) with both male and female function (perfect); bracteate base of each head (involucre) cylindrical, base of the involucre with several rows of small bractlets below the 2 rows of larger, narrow bracts (phyllaries), which are equally long, or nearly so; base of the involucre often broader in fruit.
Fruit dry, a flattened, ribbed, plumed, achene (Cypselae); plume (pappus) is attached to the expanded tip of the achene and has 2 rows of very fine (capillary) bristles adapted for wind dispersal (Flora of North America, FNA Vol. 19, 20 and 21 Page 216, 258, 259).