Hieracium

Hieracium, commonly known as hawkweeds, is a genus of flowering plants in the family Asteraceae. The genus belongs to the tribe Cichorieae and is characterized by milky sap and flower heads composed of ligulate (tongue-shaped) florets that are typically yellow.

Species are herbaceous perennials or biennials, often forming a basal rosette of hairy leaves. Stems are typically branched, with alternate leaves; inflorescences are loose panicles bearing multiple heads. The fruits are achenes with a pappus of hair for wind dispersal.

Reproduction is notable for widespread apomixis in many species, producing seeds without fertilization. This, together with frequent hybridization, has led to a large number of often poorly defined microspecies and substantial taxonomic complexity.

They are native to Europe and temperate Asia, with many species introduced elsewhere, including North America, where some hawkweeds behave as invasive weeds in pastures and disturbed sites, often outcompeting grasses.

Commonly encountered in horticulture and naturalized settings, notable species include H. pilosella (mouse-ear hawkweed), grown ornamentally, and H. caespitosum (meadow hawkweed), known as a troublesome invader in parts of North America. The name Hieracium derives from Greek hierax, hawk, reflecting an ancient belief that hawks used the plant to improve vision.