Settling velocity and pollination in the grass Diarrhena obovata

By Phillip C. Klahs

Inflorescence of Diarrhena obovata

Pollination is accomplished when pollen grains, containing male genetic information, are moved between plants and arrive at a flower with female flower parts. This is an important step in plant reproduction, and development of the seed will not occur until after fertilization. The pollen of wind pollinated plants must travel through the air to reach other plants, and to be successful in this journey pollen grains need to float in the air and travel with the wind. Settling velocity is a measurement of how fast objects fall, and tells us how long something will float in the air and the distances it can travel with certain wind speeds. Weight, density, and bumpy surface features affect the aerodynamics of the pollen grain, and these attributes can work together to slow the settling velocity.

Diarrhena obovata is a flowering plant in the grass family Poaceae that utilizes wind pollination, but lives in forest understories where wind is more turbulent and slower on average than open habitats. The blooming of D. obovata flowers and the aerodynamic properties of its pollen grains have evolved to ensure successful pollination in forest and edge habitats. This study tested when the flowers of D. obovata bloomed and how fast the pollen grains can fall through a column of still air, and determined they have a measured settling velocity of 3.77 meters per second. This is the first time the settling velocity of a forest grass has been measured even though the grass family is important ecologically and economically. 

Read the scientific publication in JPE.