Weed Description: An
erect winter or summer annual reaching 6 1/2 ft in height. Seedlings develop a basal
rosette and mature plants have leaves that are entirely without petioles. Found throughout
the United States in agronomic crops, pastures, orchards, fallow fields, waste areas, and
Cotyledons oval, 2-3 mm long. Young leaves egg-shaped with toothed margins and becoming
Stems: Erect, solid, hairy,
reaching 6 1/2 ft in height.
Leaves: The mature
plant has leaves that are entirely without petioles (sessile). Leaves are 4 inches long,
10 mm wide, alternate, linear, entire or more often toothed, crowded along the stem, and
hairy. Leaves become progressively smaller up the stem.
Roots: A short taproot with a
secondary fibrous root system.
Flowers: Many small inconspicuous flower heads occur at the top of the central
stem. Individual flowers are 5 mm in diameter with white or slightly pink ray flowers and
yellow disk flowers.
Fruit: A 1 mm long achene,
tapered from the base to the apex with many small white bristles that help in wind
Identifying Characteristics: Erect plants with mature leaves that are entirely without petioles. When
mature, this weed is easily identifiable. However, in the rosette stage of growth,
horseweed might resemble other weeds that have this rosette habit, such as
Shepherd's-Purse or Virginia Pepperweed (Lepidium