Hemizonia congesta, known by the common name hayfield tarweed, is a species of flowering plant in the family Asteraceae, native to western North America.

Hemizonia congesta is a spindly, thin-stemmed annual herb growing erect to 10–80 centimetres (3.9–31.5 in) in height.

Most of the long, narrow, pointed leaves are located on the lower portion of the stem below the branching flower stalks.

The inflorescences are covered in glandular hairs and hold daisy-like flower heads.

They include: Hemizonia congesta is native to California and Oregon, where it is a common member of the flora of a number of habitats, particularly in grasslands and fields.