Abstract

Wind pollinated (anemophilous) angiosperm lineages have often converged independently on floral traits; the syndrome of traits presumably reflecting adaptation to more efficient pollen transport by wind and capture by receptive surfaces. One often-cited trait differentiating anemophiles from zoophiles is the cohesion of pollen grains into clumps, with greater clumping expected among the latter. Further, the mechanism by which grains are released remains underexplored. This thesis examines (1) whether pollen clumping can be used diagnostically to determine the vector, and (2) the hypothesis that resonance vibration of stamens in wind gusts is a mechanism of pollen release. Pollen clumping was studied intraspecifically in the wind pollinated Plantago lanceolata and interspecifically across 23 anemophilous and zoophilous species. Mean clump size was found to be well-distinguished species by vector, and the lognormal distribution was a reasonable characterization of clump size for the majority of the species examined. The stamens of P. lanceolata were manipulated in the laboratory and observed in the field to characterize their dynamic response to vibration. Stamens had elastic properties corresponding to modeling as underdamped cantilever beams and to theoretical ranges predicted to initiate resonance vibration in wind gusts. Pollen was released in multiple discrete bursts from resonating stamens with successively greater energy requirements. In the field, pollen release was observed from a resonating stamen. Understanding the function of stamen properties is crucial for developing an evolutionary theory of anemophily and modeling the wind pollination process. This study demonstrates that anemophilous stamens have distinct, quantifiable physical properties differentiating from stamens evolved for other mating systems.