On December 11, 1981 in Tucson AZ; the USPS issued this se-tenant of four stamps depicting U.S. desert plants. Three of the plants are in the cactus family and one is an agave plant, which most botanists assign the lily or the agave family. Listed are: Agave (Agave deserti) the Saguaro (Cereus giganteus), the Beavertail Cactus (Opuntia basilaris) and the Barrel Cactus (Ferocactus wislizeni). All of the plants are succulent plants as each has fleshy tissues designed to conserve moisture. These stamps were designed by Frank Waslick.
These are real USPS postage stamps that are accepted by the Postal Service as payment for mail however the rates on the stamps must equal or exceed the current appropriate postal mailing cost or extra postage must be paid for if using them for mailing.
The stamp set shown in the picture is a stock photo and is likely not a picture of the exact stamp set you will receive in that it may differ in plate number and/or orientation. However the item you will receive will be similar including having a plate number (if one is present in the photos) and the same number of stamps.