September in Lake County, Illinois is a month of big sky punctuated by tips of tall prairie plants in an array of autumnal colors. Before the trees really get going with their own colorful show, sparks of bright yellow from the many varieties of goldenrod (Solidago spp.) dominate the open spaces. Most of the summer these plants go unnoticed, adding merely another green hue to the lush surroundings, but September is their time to shine. What may also go unnoticed, even now as goldenrod demands our attention, is the hidden world inside each plant in the form of a gall.

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