CONVERGENCE OF FILIFORM POLLEN MORPHOLOGIES IN SEAGRASSES - FUNCTIONAL MECHANISMS

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, rev eals that reproductive strategy alone does not provide sufficient info rmation 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 physi cal and empirical scrutiny. Conversely, a biophysical model, which req uires pollen to obey the fluid dynamic principles of boundary-layer fl ow, may be complicated conceptually, but it is consistent with mathema tics and nature. The correct modelling of pollination mechanisms in se agrasses provides an understanding of contemporary adaptations as well as the processes that selected them.