A moon tree is a tree which has been grown from seeds which were sent into space with Apollo 14 in January 1971. These tree can be found in many odd corners of the world, as they proved to be extremely popular with people on Earth, and in addition to the original moon trees, there are a number of second generation specimens grown from cuttings. The National Aeronautics and Space Administration (NASA) is actually in the process of trying to track down all the moon trees, as poor records were kept in the 1970s when they were distributed.
The story of the moon trees begins with Stuart Roosa, who worked as a smoke jumper for the United States Forest Service, and later as an Air Force test pilot. He was offered the opportunity to train as an astronaut and took it, being added to the crew roster for Apollo 14. All of the crew members on the flight were allowed to take along a few small personal items, and Roosa declared that he wanted to take tree seeds.
In cooperation with the Forest Service, Roosa carried hundreds of loblolly pine, sycamore, sweetgum, redwood, and douglas fir seeds on the flight. Staff at the Forest Service were curious to know what would happen to the seeds after traveling in space, and NASA thought it might be a good public relations campaign, connecting people to the space program with a moon tree in every major community. Roosa orbited the moon alone with his seeds while his companions worked on the moon's surface, and then the three returned to Earth, where the canister of seeds accidentally broke, raising concerns about their viability.
Roosa separated the seeds by species and sent them off to Forest Service biologists, who managed to germinate almost all of them. Immediately, requests for moon trees started pouring in. A common feature at many American bicentennial celebrations was a moon tree, and the moon tree proved to be popular with foreign dignitaries as well. Moon trees were planted in many American cities and sent to places like Japan, Brazil, and Germany, among others.
The United States Forest Service couldn't meet the moon tree demand, so it started propagating from cuttings to create a second generation of the trees. As the trees mature, they are not noticeably different from their Earth counterparts, and one would not know that a tree is a moon tree unless the tree happens to be marked with a plaque. Many of the species chosen are extremely long-lived, so chances are good that many of the moon trees are still alive.
Although it may seem astounding, NASA largely forgot about the moon tree program until a few curious people contacted the agency to see if they could get cuttings. Dave Williams at the Goddard Space Center rose to the occasion, trying to track down the moon trees and keeping an exhaustive list of all the verified moon trees around the world for people interested in this event in NASA's history. Williams didn't have to look very far for his first moon tree, as there is a sycamore on the grounds of the Goddard Space Center.