New leaves on a plant emerge from a rounded growing tip that consists of an outer shell covering a squishy core. One theory for these patterns is that they are driven by mechanics. Other cacti, sunflowers, and pinecones display this or other triples of Fibonacci numbers. These are three consecutive numbers from the Fibonacci sequence. The round head of a cactus is covered with small bumps, each containing one pointy spike, or “sticker.” For some cacti, you can start at the center and “connect the dots” from each sticker to a nearest neighbor to create a spiral pattern containing 3, 5, or 8 branches. Now a mathematical model published in the 23 April PRL suggests that these spiral patterns, and the Fibonacci relationships among the spirals, arise out of simple mechanical forces acting on a growing plant. The intricate spiral patterns displayed in cacti, pinecones, sunflowers, and other plants often encode the famous Fibonacci sequence of numbers: 1, 1, 2, 3, 5, 8, …, in which each element is the sum of the two preceding numbers. The three sets of spirals have 3 branches (red), 5 branches (yellow), and 8 branches (brown)–three numbers that form a so-called Fibonacci triple. Computer simulations (bottom) can reproduce the spiral patterns in a cactus (top) by calculating the forces in the growing plant and finding the most stable arrangement.