Blackthorn flowers. Several flowers on a twig from a blackthorn bush (Prunus spinosa). They are open, showing the central reproductive parts (mostly stamens). The top of the stamens are the anthers (yellow). These release pollen for transfer from flower to flower as part of the formation of a seed from which a new blackthorn bush will grow. Blackthorn flowers (or blossoms) form during a short flowering season. Fertilized flowers become the berries that contain the plant's seeds.