filotaxi

Filotaxi, also spelled filotaxia in some languages, is the pattern of arrangement of leaves, and sometimes fruits, seeds, or other organs, along a plant stem or inflorescence. It is a central topic in botany because the arrangement influences light capture, shading, water runoff, and reproductive success. The term derives from Greek phyllon (leaf) and taxis (arrangement).

Patterns observed in filotaxi include alternate leaves (one leaf per node), opposite leaves (two leaves per node), and whorled leaves (three or more leaves per node). In many plants, leaves are arranged in spiral phyllotaxis, with a constant divergence angle between successive leaves. Common spatial patterns correspond to fractions such as 1/2, 2/5, 3/8, and so on, often linked to Fibonacci numbers. The divergence angle is frequently close to the golden angle, about 137.5 degrees, which is thought to optimize light exposure and minimize shading among leaves.

Filotaxi is studied in botany and horticulture to understand developmental rules, genetic control of plant form, and adaptive strategies. It helps predict the arrangement of inflorescences and seed heads, and deviations from regular patterns can indicate mutations or environmental influences. Modern research employs image analysis, computer modeling, and comparative studies across species to describe and explain phyllotactic patterns.

Historically, filotaxi has been a focal point in investigations of plant form, with observations that many spiral arrangements exhibit regular mathematical relationships, including connections to the Fibonacci sequence and the golden ratio. This interplay between biology and math has made filotaxi a classic example of natural optimization.