Stamens 2, white. Style 1 with a plumose white or purple-tinged stigma. Barbed spines on the hypanthium elongate after fertilization. Ovary superior, matures before stamens. Flowers in a head mature sequentially from the base to the apex.
Spines are red when fruits are immature and have short, backwards pointing barbs at their tips.
At maturity fruiting heads form round burs , 3-3.5 cm diameter , that disperse as units. Most fruits are not dispersed beyond the vicinity of the parent plant, and a mat of lodged fruits can develop in the existing vegetation. Clinging burrs have the potential to be transported great distances. Overwintering leaves die shortly after new shoots begin to develop. Petiole bases of dead leaves persist for at least 3 years.