Fibonacci today is remembered for two major advances in mathematics, both found in his book Liber Abaci (The Book of Calculation), published in 1202. Ironically, he created neither of them.

Flower petals, the majority of flowers in nature have a number of petals from the Fibonacci sequence. It can have 1, 3, 5, 8, 13, or even 21 petals; some have 4, 6, or 7 petals.

Plants show Fibonacci numbers going upto 233 in sunflowers. It’s a very striking phenomenon — Alan Turing wrote computer programs seeking to understand this.