http://www.poetryfoundation.org/poem/175784. A brief biography of Williams and references may be found here: http://eretzsongs.blogspot.com/2014/08/the-songs-of-eretz-poet-of-month-for.html.
Poems about flowers are SO 18th century. Accordingly, a contemporary poet who chooses a flower as a subject is certainly taking his chances with his readership, the only exception being using the flower as a conceit in a love poem to woo women--that still works. There does not appear to be a conceit in "Queen-Anne's Lace;" it is simply a poem about the weed. Perhaps the poet mocks the flower poem genre (or is just showing off) by "elevating" a weed to the level of the red, red rose.