The liberty tree was a specific elm in Boston; it was also a generic designation for a dozen-plus gathering-sites in various colonies. And it was a stylized tree in the form of a "liberty pole," and a design element for flags. It represented American freedom.
The liberty tree also had a metaphorical inverse. Abolitionists named it the "tree of slavery," and portrayed it as an invasive non-native species. Drawing on the Bible, antislaveryites condemned the corrupt tree's "evil fruit." The fruit could symbolize any number of things, including political corruption, the assassination of Abraham Lincoln, miscegenation, unfree labor—or the presence of black people on free soil.
From their British counterparts, American abolitionists borrowed the popular Victorian literary metaphor of the tropical "Upas tree" (Antiaris toxicaria) that produced a deadly poison. Early members of the Republican Party spoke of girdling, uprooting, or felling the toxic tree of slavery.
As a graphic, the tree of slavery only occasionally appeared in nineteenth-century publications. The most striking example was cartographic. An 1888 chart by mapmaker John F. Smith titled Historical Geography attempted to explain all of U.S. history as two divergent plant growths. The godly "Tree of Liberty" had been planted in Plymouth in 1620 and its blessings spread straightly westward to the Golden Gate under the arboricultural care of Whigs and Republicans. Concurrently, the devilish "Tree of Slavery" took root in Jamestown with the arrival of the first slave ship, and twistingly spread its curses throughout the South. On his politicized map, Smith portrayed the Emancipation Proclamation as an ax in time.
This graphical and metaphorical tree never materialized in woody form—unless you count the hundreds of lynching trees across the American landscape, from California to Iowa to New York. There is no "original" Tree of Slavery to match the historic site of the Liberty Tree in Boston. If there were such a monument, it too might belong in Massachusetts, in commemoration of the enslavement of Native peoples by Puritans. In the landscape of American memory, slavery remains everywhere yet nowhere, an invisible canopy casting a malign umbrage.