Composite Flower Structure
Asters are members of the Asteracea (pronounced: aster-ai-sea-ai) or aster family of plants (formerly known as the Compositae; those taxonomists at work again!). This is one of the largest and most diverse families of plants, including such plants as sunflowers, black-eyed susans, coneflowers, daisies, thistles, dandelions, bur-docks and ragweeds. The main characteristic of the Asteracea is the composite or compound nature of their flowers, or more properly their "inflorescences". An inflorescence is an arrangement of flowers in a cluster. What we would call an individual "flower" on an aster or sunflower is, in fact, a dense cluster of many tiny flowers, called "florets". Look closely at an aster, daisy, sunflower or any other member of the Asteracea and you can see the individual florets. They can be seen clearly in the image of a Rough False Sunflower (Heliopsis helianthoides) above. Most of the florets, that form the centre or disc of the "flower", are tubular in shape and have no petals. Around the edge of the "flower" are florets which have a single petal attached to their outer edge. This array of single-petalled florets encircling the other densely packed florets appears to us to be a single "flower". The whole inflorescence sits in a cup-like structure called an involucre, which is a whorl of bracts (scaly, leaf-like structures) below the "flower".
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