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Name: American Holly (Ilex opaca)
Range and typical habitat(s): Typically southeastern United States, from eastern Texas to the Atlantic coast, southern Missouri, and central Florida to scattered portions of New England. iNaturalist observations also place it in portions of Michigan, Illinois, Ohio, and Oklahoma, showing some expansion compared to the 2014 BONAP map, so its range may be expanding in response to climate change. In most of its range it is an understory tree growing in the shade of larger species. However, in Florida’s scrub habitat it grows as a shrub.
Distinguishing physical characteristics (size, colors, overall shapes, detail shapes): At first glance American holly looks quite similar to the European holly (Ilex aquifolium) so commonly used got holiday decorations (more about the differences between the two below.) It has medium to dark green oval-shaped leaves, sometimes with a yellowish tint, whose margins (edges) have concave curves between sharp points that are regularly spaced; large leaves may reach three inches long.
The American holly’s leaves have a leathery, stiff texture, and may appear waxy, and the underside is paler, often yellow in color. Each leaf has a central vein (midrib) that is depressed, appearing almost like a deep crease. Thinner veins branch off of both sides of the midrib. Some leaves may display smooth margins instead of the more typically spiky ones, especially when they are high enough to be out of the reach of browsing herbivores like deer.
The foliage stays green throughout the year rather than being shed in fall; a given leaf may stay on the tree for up to three years before being displaced by a new replacement leaf. The leaves grow in an alternate pattern along a twig, with each leaf growing a little further along the twig than the last. The tree’s branches and trunk are covered in pale gray bark that is relatively smooth, but may have horizontal and vertical striations, along with various nodes and bumps, and might also play host to white patches of microlichen colonies. Other lichens, as well as mosses, also may add color to the American holly’s bark.
An exceptional specimen of American holly can reach almost 100 feet tall when mature, though it grows slowly. Such large trees are generally a century or more old, and the oldest on record was just a few years shy of 150.
The flowers of American holly are small (1/2″ or less across) with green centers and four (sometimes six) white petals that are broad with a rounded end, and whose tips curve back toward the plant. They grow in clusters of several flowers sprouting from one spot. American holly is dioecious, meaning that there are female and male plants; the males tend to reach sexual maturity a few years earlier than the females, but they all are generally reproducing by the age of ten.
When fertilized by insects the female flowers then turn into the well-known red berries. Technically these are drupes rather than true berries, with four seeds apiece, and while they start out green they ripen to a bright red. The berries are popular with birds like cedar waxwings (Bombycilla cedrorum), but are toxic to humans and our pets.
Other organisms it could be confused with and how to tell the difference: Due to their similarity, American holly and European holly may easily be confused at first glance, and both prefer the understory of a forest. However, the European species does not grow as large. The leaves of European holly are darker and have a glossier appearance; the edges may also be more warped where those of American holly lie comparatively flat. Moreover, European holly grows more commonly along the west coast of North America, and is more sparse throughout American holly’s native range, especially outside of cultivated spaces.
Yaupon holly (Ilex vomitoria) is another species native to the southeastern North America, particularly the Gulf Coast states and the southern third of the Atlantic coast. It is a much smaller shrub that rarely exceeds thirty feet tall, and its leaves are round with serrated or scalloped edges rather than the pointed margins of American holly. The petals of the flowers may not curve as much as on American holly.
Dahoon holly (Ilex cassine) also grows in the extreme southeastern United States, from Louisiana to the southern tip of North Carolina, and primarily along the coastline except in Florida where it can be found across much of the peninsula. Its leaves are longer and more slender than those of American holly, and the margins are almost entirely smooth except for a series of very small spikes.
Possumhaw (Ilex decidua) has long, slender leaves with a gently pointed tip and serrated edges. This deciduous plant drops its leaves in fall, unlike the evergreen American holly.
There are other plants that have similar leaves to American holly but that grow out of its range, such as the various species of Oregon grape (Mahonia spp.) in the Pacific Northwest, and holm oak (Quercus ilex), for which the genus Ilex was originally named.
Further reading:
North Carolina Extension Gardener Plant Toolbox: Ilex opaca
Missouri Botanical Garden Plant Finder: Ilex opaca
Native Plant Trust: Ilex opaca – American holly
University of Connecticut Plant Database: Ilex opaca
