hawkweed, any species of the genus Hieracium of the family Asteraceae (aster family), widely distributed perennials, chiefly of open fields. The small, dandelionlike flower heads are borne in clusters at the top of a long, hairy stem; the basal leaves are also hairy. Some species of the W United States are used for forage; in the East, hawkweeds are generally considered pests. In the fall the orange hawkweed, or devil's-paintbrush, the rattlesnake weed, and the king devil often turn whole fields a ruddy orange or yellow. Other species are red or white; a few are cultivated in rocky soil where other plants cannot grow. In folklore, hawks sharpened their eyesight by eating hawkweed sap. Hawkweed is classified in the division Magnoliophyta, class Magnoliopsida, order Asterales, family Asteraceae.

Any of the approximately 200 species of weedy plants that make up the genus Hieracium, in the composite family, native to temperate regions. Mouse-ear hawkweed (H. pilosella), orange hawkweed (H. aurantiacum), and common hawkweed (H. vulgatum) are widely distributed weeds. Some species are cultivated as garden ornamentals for their attractive flower clusters.

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