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The Tallgrass Prairie in Illinois


Prairie Plant Terminology — Flower Heads of the Sunflower Family (Asteraceae)


In the sunflower family (Asteraceae), what looks like a single flower is actually a flower head composed of many small flowers. Each flower has sepals (modified into pappus), petals, stamens, and a pistil. In a typical member of the sunflower family, there are two different types of flowers. The "petals" that are around the edge of the flower head are the ray flowers. In the center of the flower head are many disk flowers. Found at the base of each disk flower is a small structure called thechaff (not always present). The base of the flower head is the receptacle. Underneath the complete flower head are green sepallike structures called phyllaries, which are modified leaves. Some plants, like blazing stars (Liatris species) have only disk flowers. Other plants, such as dandelions (not pictured) have only ray flowers.


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