Thistle bud. (3rd of 5 images) Close-up of the bud of the cotton thistle (Onoperdum acanthium) opening into flower. 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 thistle is a tall plant with spiny leaves and stems. It is commonly found on waste ground and bare areas, preferring sandy soil. The flowers appear between July and September. See photos B539/030- 034 for sequence of flower opening and seed development.