Answers to these questions I have received about holly make a perfect column for the holiday season.
Q: Are holly trees native to North America? How big do holly trees get? Where did the idea of using holly at Christmastime originate? Why do holly leaves have those needlelike spines on them?
A: The American holly, scientific name “Ilex opaca,” is native to the southeastern sector of the United States from New England to the upper half of Florida to eastern Texas. Hollies also occur naturally in Pennsylvania, West Virginia and southern Missouri.
Nearly everyone knows what a holly tree looks like, but they can reach sizes that may surprise you. American Forests, an outstanding conservation organization, has a National Big Tree Program that identifies the largest individual trees of every species in the United States. Several champion-size holly trees vie for the record. A tree at the Chelsea Historic Site, Md., is a co-champion because of a combination of criteria (height, trunk circumference, and crown spread).
The tallest holly, in Alexandria, Va., measures 68 feet from the ground to the top branch (about as tall as a six-story building). American Forests’ website lists a holly in Chattooga Co., Ga., as the one with the largest circumference (148 in), whereas the downloadable fall 2012 edition of the “National Register of Big Trees” cites a tree in Arlington, Va. (154 in). In either case, two tall men could barely reach around the trunk and touch their fingers. American holly trees grow slowly, but they can get really big.
A closely related species, the European holly with the scientific name “Ilex aquifolium” became associated with the Christmas season centuries ago. Like the American holly, the European holly has glossy green, waxy leaves and bright red berries in winter. A hardy plant whose branches could be brought indoors to liven up a bleak winter day, holly was probably first used as decoration by pagan cultures, including the Druids. Christians also liked the holly’s cheerful display and before long it became a common decoration in many parts of the world, including America. Today, a variety of cultivated varieties of the two species are commercially produced in many regions.
From an ecological perspective, European and American holly trees have a common trait – a holly tree is either male or female, and the two sexes differ dramatically. Only the female trees have the bright berries; the male trees simply have the shiny green, pointed leaves. Bees, wasps, and other insects pollinate holly trees, and unless a male tree is nearby, the fruits, that is the berries, of the female tree cannot develop. So, even though the female tree is the one we consider most impressive and we prefer for our Christmas wreathes, no berries will appear unless an unassuming male is in the vicinity.
As for the ecological explanation for why holly leaves have those needle-sharp points on the end and sometimes on the sides, the scientific jury is still out. Some grazing animals might be deterred by having to bite around a pointed spine, so one idea is that they prevent animals such as deer from eating them. One proposal, which I checked out on a holly tree in my backyard, is that the lower leaves have more spines than the upper ones – the supposition being that grazing deer would be more likely to eat the lower leaves. Indeed, on my holly tree, most leaves 10 feet above the ground had fewer spines, but we need more data than my casual examination of a single tree. Another idea is that the spines are a perfect conduit for freezing rain to run off during an ice storm, a useful trait for an evergreen tree like holly whose leaves might break if they were weighted down with ice.
Whatever the explanation may be for the pointy leaves, a few branches of holly, with or without the colorful berries, can add a festive touch to your holiday decorations.
Send environmental questions to firstname.lastname@example.org.
Whit Gibbons is an ecologist and environmental educator with the University of Georgia’s Savannah River Ecology Laboratory.