AppearanceCentaurea calcitrapa is a biennial to perennial plant. It grows 2-3 ft. (0.61-0.91 m) tall.Foliage The stems and leaves are covered with fine hairs. Lower and basal leaves are divided or deeply lobed. Leaves become less divided toward the apex of the plant.Flowers Flowering occurs from July to October, when purple to pink blooms develop at the ends of the stems. Floral bracts are tipped with 1 in. (2.5 cm) long, straw colored spines.Fruit The fruit is an achene 0.08-0.16 in. (2-4 mm) long which lacks a pappus.Ecological Threat A native of southern Europe, Centaurea calcitrapa produces prolific seeds and often invades floodplains, dry forests and grasslands.