Tissue, please… In honor of the sneezin’ season, this CSI is common ragweed pollen as seen under a microscope. Ragweed pollen is the principal cause of hay fever and can also trigger asthma. But for all the itchy throats and watery eyes, this tough little plant is just trying to survive. The common ragweed is an annual that grows to about 3.5 feet tall, has hairy stems, divided leaves, and simple greenish-yellow flowers. Arguably not much to look at, the ragweed does not rely on the help of flying creatures to transfer pollen from plant to plant. Thus it lacks the bright, smelly flowers that attract the birds and bees. The ragweed relies on a process called wind pollination to procreate. The light, powdery pollen forms in the anther, or male part, and breezes through the air to the pistil, or female part, where fertilization occurs. Structurally, the pollen grain is multi-layered. The outer layer, or exine, not only protects the center nuclei responsible for fertilization, but also makes the grain virtually indestructible. A single ragweed plant can generate a million grains of pollen each day during its peak season, mainly late summer and early fall. Not all pollen reaches its intended destination in the pistil and instead lands in the human nose and many geologic sediments. In fact, grains of ragweed pollen have been found 400 miles out to sea and 2 miles high in the air. By studying geologic pollen sediments scientists have been able to make remarkable discoveries about the origin and evolution of plant life.
Pollen image courtesy of NIAID.