I was birding on a boardwalk in Apalachicola when I photographed this flower.  I later showed it to a University of Florida Extension Agent, and he identified it as Poison Hemlock.  Then I was glad I had only photographed it and not tried to examine it.<br />
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UPDATE: This flower has been identified as Water Hemlock (Cicuta maculata).  It is even more poisonous than Poison Hemlock, in fact it might be the most poisonous plant in North America.