Hemizonia congesta is a species of flowering plant in the daisy family known by the common name hayfield tarweed. It is native to California and Oregon, where it is a common member of the flora in a number of habitats, particularly grasslands and fields. This is a spindly, thin-stemmed annual herb growing erect to 10 to 80 centimeters in height. Like other tarweeds the stem and foliage are hairy and have an odor reminiscent of tar. Most of the long, narrow, pointed leaves are located on the lower portion of the stem below the branching. The flower clusters are covered in hairy hairs and hold daisylike flower heads. Each head has a center of yellowish dark-tipped disc florets and a fringe of bright yellow to white ray florets, often with purplish striping on the undersides. The ray florets are toothed or lobed on the tips, with the middle tooth thinner than the others. There are many subspecies which can vary in appearance.