21d Money for party politicians (6) ?R?E?S Greens?
25d Summer herbaceous plant cut from beginning of May (5) A?D?R has to be Adder. The plant is Madder and you lop off the M but where is any reference to a snake in the clue?
Greenbacks were paper currency issued by the United States during the American Civil War. They were in two forms: Demand Notes, issued in 1861–1862, and United States Notes issued in 1862–1865