Postage stamps have long been a tiny platform for surprising creativity, a small square of delight in daily life. Even though we can text, email, or FaceTime, receiving a letter or a postcard still feels intimate, especially if the stamp is, well, special. Over the years, the American Postal service has used flowers and elements from the garden on its stamps, a nod to the country’s incredible biodiversity as well as an acknowledgment of nature’s most impressive botanicals. Here is an online retrospective of those stamps. —E.C.