Centaurea cyanus
Bachelor's button, cornflower, Cornflower
(c) Douglas Goldman, some rights reserved (CC BY-SA), uploaded by Douglas Goldman · licence
Family: Asteraceae · Type: Herb · Not Native
Centaurea cyanus (Bachelor's button) is a non-native California herb in the Asteraceae family, recognized by blue flowers and radiant heads with prominent sterile flowers.
Bachelor's button is a naturalized annual found in California's Central Valley and Coastal Ranges in grasslands, open woodlands, and disturbed areas at elevations generally up to 1,500 meters. Flowering from April to September, this plant produces striking blue flowers (occasionally white to purple) with radiant heads 10 to 16 millimeters wide, featuring fringed green or purple phyllary tips with white to black teeth. Growing 20 to 100 centimeters tall with a single erect stem that branches toward the top, it has an open, panicle-like cluster of flower heads. Its leaves are green to gray, thinly to densely covered in soft hair, with lower leaves reaching 3 to 10 centimeters long and often entire or few-lobed, while upper leaves are linear and minimally toothed. The fruit is 4 to 5 millimeters long, straw-colored with a hint of blue, and covered in fine short hairs.
Identification and appearance
Key characters: 15 sympatric species; blue flowers and radiant heads with prominent sterile flowers are diagnostic
Habitat and range
Habitat: Grassland, open woodland, disturbed areas
Elevation: generally <= 1500 m
Outside California: native to southern Europe
Bloom period
Centaurea cyanus blooms Apr-Sep.
How to tell it apart
vs Cirsium: Cirsium bracts taper to simple spines; Centaurea bract tips expanded with fringed/toothed edges; vs Carduus: Carduus bracts spine-tipped but not fringed; Centaurea bract appendages distinctly fringed or toothed; vs Jacobaea: Jacobaea has obvious yellow ray flowers; Centaurea lacks true rays (all tubular flowers); vs Silybum: Silybum has white-veined leaves and simple spine-tipped bracts; Centaurea bracts ornately fringed; vs Eriophorum: Eriophorum is a sedge with grass-like leaves and cottony heads; Centaurea is a branched herb
Frequently asked questions
Is Centaurea cyanus native to California?
No. Centaurea cyanus is not native to California (recorded as not native).
When does Centaurea cyanus bloom?
Centaurea cyanus blooms Apr-Sep.
What plant family does Centaurea cyanus belong to?
Centaurea cyanus is in the Asteraceae family, genus Centaurea.
What habitat does Centaurea cyanus grow in?
Centaurea cyanus grows in Grassland, open woodland, disturbed areas.
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · Index of California Plant Names · CalPhotos
Last updated 2026-10-07
Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Cal-IPC, and more.