  Circumnutations are widespread in plants and typically associated with
exploratory movements, however a quantitative understanding of their role
remains elusive. In this study we report, for the first time, the role of noisy
circumnutations in facilitating an optimal growth pattern within a crowded
group of mutually shading plants. We revisit the problem of self-organization
observed for sunflowers, mediated by shade response interactions. Our analysis
reveals that circumnutation movements conform to a bounded random walk
characterized by a remarkably broad distribution of velocities, covering three
orders of magnitude. In motile animal systems such wide distributions of
movement velocities are frequently identified with enhancement of behavioral
processes, suggesting that circumnutations may serve as a source of functional
noise. To test our hypothesis, we developed a parsimonious model of interacting
growing disks, informed by experiments, successfully capturing the
characteristic dynamics of individual and multiple interacting plants.
Employing our simulation framework we examine the role of circumnutations in
the system, and find that the observed breadth of the velocity distribution
confers advantageous effects by facilitating exploration of potential
configurations, leading to an optimized arrangement with minimal shading. These
findings represent the first report of functional noise in plant movements, and
establishes a theoretical foundation for investigating how plants navigate
their environment by employing computational processes such as task-oriented
processes, optimization, and active sensing.
