Thistle flower. (4th of 5 images) Close-up of a flower of the cotton thistle (Onoperdum acanthium). The petals (pink) protect the reproductive organs of the flower, and help attract the insects which perform the pollination. The stamens, which carry the pollen (male part) can be seen as pale pink spikes protruding from some of the petals. The female organs (carpels) are at the base of the individual flowers (white), and are protected by the spines of the flower head. The flowers appear between July and September. See photos B539/030-034 for sequence of flower opening and seed formation.