Poppies and Memorial Day

In 1947 the U.S. published a stamp which honored Moina Belle Michael for establishing the Poppy Memorial Day, which occurs the Saturday before Memorial Day.  After WWI the poppy became a symbol of the tragedy of war.  This was further engrained in our psychy after John McCrae wrote the poem Flander's Fields.  He noticed poppies growing in the burial grounds for those who had died in the war.
In Flanders Fields: John McCrae

In Flanders fields the poppies blow
Between the crosses, row on row,
That mark our place; and in the sky
The larks, still bravely singing, fly
Scarce heard amid the guns below.

We are the Dead. Short days ago
We lived, felt dawn, saw sunset glow,
Loved and were loved, and now we lie
In Flanders fields.

Take up our quarrel with the foe:
To you from failing hands we throw
The torch; be yours to hold it high.
If ye break faith with us who die
We shall not sleep, though poppies grow
In Flanders fields.

"Its references to the red poppies that grew over the graves of fallen soldiers resulted in the remembrance poppy becoming one of the world's most recognized memorial symbols for soldiers who have died in conflict"  (Wikipedia)

Michael wrote a poem responding to "In Flanders Fields"
We cherish too, the Poppy red
That grows on fields where valor led,
It seems to signal to the skies
That blood of heroes never dies.
She was instrumental in making the Poppy part of Memorial Day.  By 1922 Veterans of Foreign Wars began selling poppies.