Ambrosia trifida

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leaf--what kind of margin is present here?  Most of the time, giant ragweed has three lobes, but can range from one to five lobes (and rarely more than five). male heads, with staments just about mature (get ready to sneeze!)

mature male heads, with anthers exserted (meaning that they are stuck out of the heads), and female heads (these are hard to see--they are beneath the male heads just above the highest leaves).  Ragweeds are a major source of Fall hay fever (not goldenrods!). immature fruits--notice the bracts underneath the fruits

mature fruits in Fall, still surrounded by bracts--notice that the male heads have all fallen off, leaving only the rachis of the inflorescence behind.