This listing is for the Pane of 20 Forever postage stamps Numbering more than 4, 000 species, live on every continent except Antarctica. Of those thousands, more than 90 species are found in the United States. Digital illustrations of four North American grace these new stamps: the Pacific tree frog, the northern leopard frog, the American green tree frog, and the squirrel tree frog. Working with a primarily green color palette, the artist captured the essence of each animal with enough important defining features to make each recognizable. stamp is being issued as a Forever postage stamp. This stamp will always be equal in value to the current one-ounce First-Class postage rate.