For more than a century, the Liberty Tree grew unnoticed on Boston Common. The innocuous elm’s claim to fame came in 1765, when the British imposed the Stamp Act, which instituted a tax on printed materials in the colonies. Calling it censorship, colonists began to demonstrate and one activist group, the Sons of Liberty, gathered under the tree’s limbs, adorning them with banners and lanterns—and, later, effigies of tax collectors.

The idea of a Liberty Tree caught on and soon 13 trees dotting the eastern seaboard carried the name. Colonists probably thought milling around under trees appeared less seditious to the Brits than meeting in public buildings. But in 1775, a group of loyalists had had it, and chopped down the tree on Boston Common.

Nearly two centuries later, the tree had vanished from collective memory. All that remained was a dirty plaque hidden by a hamburger joint sign. A Boston Herald reporter in the 1960s brought to light the tree’s connection to the founding of the U.S. and convinced Gov. John Volpe and the Boston Redevelopment Authority to erect a plaque in a small plaza at Boylston and Washington streets.

“Trees have strong romantic value,” says Phyllis Andersen, landscape historian and former director of the Institute for Cultural Landscape Studies of the Arnold Arboretum. The Liberty Tree in Boston was likely nothing special back in the day: It was just an elm, a common native tree widely planted in the 17th and 18th centuries. “It is around the human drama that the tree gained its value,” Andersen says.

What landscape historians like Andersen find valuable in a tree are its age, its association with an important person or event, or its added design significance in an important garden.
The so-called “Witness Trees” that have survived near Civil War battlefields are valued as onlookers to the battles. Trees like the “Gettysburg Address Honey Locust” and “Manassas Horsechestnut”—diligently cross-referenced with old surveys and photographs—won the favor of Civil War buffs and environmental organizations alike. These groups want to make sure the trees are remembered—and by something more than a plaque.

Before a tree dies, a propagule of that specific tree can be planted, resulting in a genetically identical new tree. Not only are descendants of the Witness Trees available, but sentimental gardeners can also find saplings that are said to be direct descendants of the FDR Rosebud, the Harriet Beecher Stowe White Ash, or Johnny Appleseed’s own apple tree. Living “trees of significance” that have been cloned include an American linden at the Longfellow National Historic Site in Cambridge, Mass., that predates Longfellow’s residency and a yellowwood planted by John Quincy Adams at the Adams National Historic Site in Quincy, Mass.

As with other forms of cloning, there is some debate around such propagation. Say you want a romantic souvenir of the white ash that witnessed Harriet Beecher Stowe’s speeches. White ash is prone to disease, so many scientists and landscape historians agree that it is better to plant a disease-resistant hybrid than a clone, Andersen says. Preservationists might argue for the genetically identical one, saying we need this kind of symbol in order to hold on to our past.

The original trees are considered “primary objects” in our nation’s history, according to Andersen. They weren’t manipulated or planted—they simply were present during events we know happened as well as ones that will forever remain a mystery to us. The question is, exactly how tightly do we hold on?