Spiral aloe, Kangaroo Island, Australia

© Michael Melford/Alam

Nature's secret code. Fibonacci Day

On Fibonacci Day, mathematicians and scientists honour one of their own: Leonardo Bonacci. More commonly known as Fibonacci, the medieval mathematician is notable for popularising the Hindu-Arabic numeral system, with its use of zero, decimal points and 10 numbers instead of the ponderous Roman numeral system. He's most famous, however, for his sequence of numbers: 0, 1, 1, 2, 3, 5, 8... By adding the first two numbers, you arrive at the third, and adding the previous two numbers, you arrive at the next number, and so on. Disregarding the zero, the first four numbers correspond to today's date, 11/23.

The number sequence also corresponds to the golden ratio. This mathematical phenomenon is found in nature, including the spiral shapes of nautilus shells, sunflower seeds, pinecones and the leaves of the spiral aloe plant in today's image. The spiral aloe grows on mountainous slopes at an altitude between 2,000 and 2,599 metres. It's highly sought after because of the spiral pattern of its leaves, but it's difficult to cultivate and usually dies outside of its natural habitat.