Biennial or short-lived perennial, from the Asteraceae family, Centaurea calcitrapa is widespread throughout the Mediterranean basin and has become naturalized well beyond, in Central Europe, Western Asia, and North America. It grows on wastelands, roadsides, dry lawns, and disturbed calcareous soils, from sea level to moderate altitudes.
It forms sprawling clumps with sinuous and arched stems, reaching 30 to 60 cm in height. The leaves are lanceolate to pinnatifid, bluish-green, slightly wavy at the edges. The flower heads, sessile or nearly so, are inserted directly at the axils of the upper leaves, an immediately recognizable feature that distinguishes it from most other knapweeds.
The involucre is the most striking element: it is armed with long, robust spines, straw-yellow at the base, radiating star-like and exactly reminiscent of the caltrop, that medieval war device with multiple spikes that the Latin name calcitrapa unequivocally designates. The flowers are pink-lilac to bright pink, the peripheral ones slightly enlarged.
In its natural habitat, flowering extends from June to September.
Little cultivated in gardens, it can find its place in a dry rockery in full sun, on well-drained calcareous soil, for the enthusiast of Mediterranean wild plants with a strong character. It reseeds easily.