On March 19, 1998, the USPS issued a set of 5 stamps that depict 5 types of flowering trees, including dogwood, magnolia, crab apple, poplar, and paloverde.
These 5 stamps are on 5 unaddressed first day covers, cacheted in color by Fleetwood. Each cover has text on the back that describes the stamp on the front.
This set of 5 would be a great addition to any FDC collection!
See the scans for details.