Helianthus annuus

Common Name:  Common Sunflower

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habit head--sunflower heads are large!  do you see the stamens on the open disk flowers (they are the black columnar structures)?
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this head has been completely pollinated--the ray corollas will soon fall off and each disk flower will produce a single fruit (which we commonly call sunflower seeds) leaf--just like the heads, the leaves are huge too!
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stem showing hairs--these hairs make the stems feel extremely coarse (the leaves also feel coarse) Helianthus annuus, as the name implies, is an annual species of sunflower.  Thus, the young plants grow from seed, grow, flower, and set fruit within one year.  This young plant was photographed in early April...
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...and had grown to approximately 7 feet tall by late May! This is a picture of the same plant in peak flower in mid-June.   Sunflowers are prolific breeders, and you can expect this plant to produce at least hundreds of seeds!