Prickly lettuce (Lactuca serriola)
Prickly lettuce is a common winter annual or biennial broadleaf plant that germinates with the onset of winter rains and inhabits gardens, agricultural land and many other areas.
It can be found in annual grasslands, seasonal wetlands, ditchbanks, fields, agronomic and vegetable croplands, orchards, vineyards, landscaped areas, urban places, roadsides, and is a prolific colonizer of disturbed habitats.
Cotyledons (seed leaves) are football shaped to egg shaped, often have slightly indented tips, have bases that abruptly taper into a short stalk, and usually have a few fine, gland-tipped hairs, especially on the edges. The first and later leaves are egg to football shaped, have smooth edges or are weakly toothed, have rounded tips, and have bases that gradually taper into a short stalk. Leaves are alternate to one another along the stem and are mostly 2 to 2-1/2 times longer than wide. Leaves that form the rosette have stiff bristles on the lower midvein.
Young plants exist as basal rosettes until the flowering stem develops at maturity.
The mature plant is erect and can grow up to 6-1/2 feet tall. Stems branch at the flower head. The lower portions of stems are smooth or have bristly hairs. Rosette leaves may be withered or missing at flowering. Leaves are deeply lobed or unlobed, have prickly edges, have a row of prickly bristles on the lower midvein, and are alternate to one another along the stem, clasping it. Prickly lettuce has much stiffer bristles than in other Lactuca species.
Flowers bloom from April through October. Flower heads consist of numerous pale-yellow, stalked or stalkless flowers that attach to branches that extend outward. Individual flowers look like small dandelion flowers.
Fruits are small, roughly 1/10 of an inch (3 mm) long, single seeded, lance shaped, flattened, with minutely barbed ribs, and attach to a long slender stalk that terminates in a tuft of fine hairs (bristles).
Control with corn gluten meal, improved soil, competition and spot spraying young plants with strong vinegar or fatty acid products.