Sunflower seed head (Helianthus annuus). The spiral arrangement of the seeds describe a Fibonacci mathematical series, one in which each number is the sum of the two previous numbers. For example: 0, 1, 1, 2, 3, 5, 8, 13, 21 and so on. This series was discovered by Italian mathematician Leonardo Fibonacci (1170-1240), and many natural patterns can be described using it.