This moon tree is marked with a plaque. Most are not, and many have been lost. (Photo: Courtesy National Space Science Data Center)

As a species, human beings tend to have short memories. Case in point: When it comes to moon trees, many people may not know what they are (never mind where they are), and they were planted only 40-odd years ago.

Moon trees were grown from seeds astronaut Stuart Roosa carried in his personal kit on the Apollo 14 mission in early February 1971. About 500 loblolly pine, redwood, sweet gum, sycamore and Douglas fir tree seeds went up with him and orbited the moon 34 times. (Roosa stayed on board while astronauts Alan Shepard and Edgar Mitchell made the third moon landing.)

Roosa had been a smoke jumper (that's a forest fire first responder) for the U.S. Forest Service prior to becoming an astronaut, and he brought the seeds not only to honor the service, but also to run a simple test: Would the seeds that had gone to the moon sprout as easily as Earth-only seeds?

About 450 of the seeds sprouted in similar numbers and as typically as their Earth-only control seeds. After a few years of care at NASA, the now-baby trees were planted in locations across the United States, many as part of the 1976 bicentennial celebrations.

Where the trees are

According to NASA, "A loblolly pine was planted at the White House, and trees were planted in Brazil, Switzerland, and presented to the emperor of Japan, among others. Trees have also been planted in Washington Square in Philadelphia, at Valley Forge, in the International Forest of Friendship, and at various universities and NASA centers." You can find a list of all the locations in the U.S. and abroad here (since trees were southern and western species, there aren't many locations in the Northeast, though there is one in New Jersey and one in Massachusetts).

This plaque identifies a sycamore as a moon tree. (Photo: A Geek Mom /flickr)

And then, for decades, they were forgotten, and many were lost.

A few of the trees have died (including the loblolly pine in Washington, D.C.), but many are still growing. Trees that have grown from cuttings from the original moon trees are called "half-moon" trees.

In the early 2000s, NASA tried to compile a list of moon trees, but there are only about 75 of the original 400+ on the list, which means there are hundreds of moon trees out there that have probably been lost forever.

Roosa died in 1994, but a moon sycamore grows at his grave at Arlington National Cemetery.