The U.S. House of Representatives voted to make the rose the “national floral emblem” in 1986. New York (NY) Times columnist William Safire (1929-2009) wrote on September 25, 1986:
 
“No one flower can ever symbolize this nation. America is a bouquet.”
 
 
Wikipedia: William Safire
William Lewis Safire (/ˈsæfaɪər/; December 17, 1929 – September 27, 2009) was an American author, columnist, journalist, and presidential speechwriter.
 
He was a long-time syndicated political columnist for the New York Times and the author of “On Language” in the New York Times Magazine, a column on popular etymology, new or unusual usages, and other language-related topics from its inception.
 
New York (NY) Times
ESSAY; Under the Rose
By William Safire
Published: September 25, 1986
WASHINGTON— The House of Representatives, after two minutes of discussion and by unrecorded vote, approved a bill passed by the Senate after a century of debate making the rose our ‘‘national floral emblem.’‘
(...)
Americans know it is better to live in a salad bowl than a melting pot. We are better off as part of a mixture rather than a mush. What calls for semiotic celebration is not so much our unity as the strength and glory of our diversity.
 
No one flower can ever symbolize this nation. America is a bouquet.
     
Google Books
And I Quote, Revised Edition:
The Definitive Collection of Quotes, Sayings, and Jokes for the COntemporary Speechmaker
By Ashton Applewhite, William R. Evans III and Andrew Frothingham
New York, NY: Thomas Dunne Books
2003
Pg. 419:
No one flower can ever symbolize this nation. America is a bouquet. — William Sajire, regarding selection of a “national flower”
 
Google Books
1001 Smartest Things Ever Said
Edited by Steven Price
Guilford, CT: The Lyons Press
2005
Pg. ?:
No one flower can ever symbolize this nation. America is a bouquet. —William Safire
 
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No one flower can ever symbolize this nation. America is a bouquet.  ~ William Safire
4:40 PM - 11 Jun 2017