Convergence of filiform pollen morphologies in seagrasses: Functional mechanisms

Summary The peculiar filiform pollen morphology and ability to pollinate in an aquatic medium have evolved convergently in the marine angiosperms or seagrasses. A comparison of these systems with freshwater ones, reveals that reproductive strategy alone does not provide sufficient information to understand this convergence. Several models have, however, been proposed to explain the function and evolution of seagrass pollen morphologies. The first is a mathematical model, random search theory, which requires pollen to travel both randomly and perpendicularly to its path. It is elegant conceptually, but does not hold up to physical and empirical scrutiny. Conversely, a biophysical model, which requires pollen to obey the fluid dynamic principles of boundary-layer flow, may be complicated conceptually, but it is consistent with mathematics and nature. The correct modelling of pollination mechanisms in seagrasses provides an understanding of contemporary adaptations as well as the processes that selected them.