Thistle seed head. (5th of 5 images) Close-up of the flowering head of a cotton thistle (Onoperdum acanthium) after pollination, showing the seeds. The seeds (black) have a tuft of fine hair at one end. This is to allow them to be easily carried by the wind away from the parent plant. The spines of the thistle flower head protect the seeds from birds and small animals which would eat them. The thistle 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 formation.