How well do you know the American holly (Ilex opaca)? The National Arboretum has one of the largest and oldest collections of American holly cultivars found anywhere. Many of these trees are found in the Holly and Magnolia Collection. American holly populations were seriously threatened during the late 19th and early 20th centuries due to a high demand for living holiday decorations. Read a past article from Arbor Friends to learn more about the National Arboretum’s role in conserving American holly and cultivating it for landscape use.