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Summer 2010

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

goldenrod and ragweed

August 31, 2010

Goldenrod and ragweed

The back-to-school weeds

In late summer, school-bus-colored flowers appear.

The bright yellow blooms of goldenrod are hard to miss. Their vivid display corresponds with a return to the classroom and with an uptick in allergy symptoms that are commonly blamed on the flower's pollen.

But pollen from goldenrod is rarely carried by breezes. It's sticky and clings to insects, which transport it from flower to flower.

A real culprit for outdoor allergies this time of year is ragweed, which releases an airborne pollen that is a notoriously powerful allergen. Ragweed's green and inconspicuous flowers are much less noticeable than those of goldenrod, which blooms at the same time.

Goldenrod and ragweed pollen grains

Grains of goldenrod pollen, left, and ragweed pollen, right, are both about 20 microns (or 4/5,000 inch) in diameter and have a similar geometry, but they employ very different strategies for dispersal.

Sources: University of Missouri, Boston Medical and Surgical Journal