Description:
This single-trunked tree is typically 30-60' tall at maturity, forming
a rounded pyramidal crown from a dense network of short crooked
branches. On older trees, trunk bark is light gray, shallowly furrowed,
and warty, otherwise it is light gray and more smooth. Branch bark is
also light green and relatively smooth. The bark of both trunk and
larger branches is often discolored from lichens. Twigs are gray or
brown and smooth, while young shoots are light green to tan and either
glabrous or hairy. Evergreen alternate leaves occur along the twigs and
young shoots. The leaf blades are 2-4" long and ¾-2" across; they are
broadly elliptic or ovate and shallowly lobed (pinnatifid). The lobes
and tips of the leaf blades terminate in sharp spiny teeth. The
upper blade surface is yellowish green or green and somewhat shiny,
while the lower surface is more pale and dull; both sides of the blade
are hairless. The texture of the leaf blades is stiff and leathery. The
petioles are short, light green, and often pubescent.
American Holly is
dioecious, forming male (staminate) and female (pistillate) flowers on
separate trees. Male trees produce axillary clusters of 3-12 male
flowers on peduncles about 1" long. Individual male flowers are about
¼" across, consisting of a short green calyx with 4 lobes, 4 greenish
white or yellowish white petals, and 4 stamens. Female trees produce
female flowers individually or in groups of 2-3 (rarely more).
Individual female flowers are about ¼" across, consisting of a short
green calyx with 4 lobes, 4 greenish white or yellowish white petals, 4
residual stamens that are infertile,
and a green pistil. The petals of both male and female flowers are
oblong in shape. The peduncle and pedicels of the flowers are green and
either hairless or sparsely pubescent. The blooming period occurs
during late spring or early summer for about 3 weeks. Cross-pollination
between a male tree and a female tree is required in order for the
latter to set fruit. Fertile female flowers are replaced by drupes
that become mature during the fall. Mature drupes are about 1/3" (8
mm.) across
and either bright red or orange-red (rarely yellow). The fleshy
interior of each drupe has a bitter taste. This tree spreads by
reseeding itself.
Cultivation: The preference is light shade to
full sun, moist to mesic well-drained conditions, and a somewhat acidic
soil. American Holly adapts to soil containing sand, rocky
material, or loam. Flowers and fruits can be produced in less than 10
years. This tree grows slowly and can live up to 150 years.
Individual evergreen leaves persist on a tree for about 3 years before
they are replaced. Severe winter cold can cause die-back
of branches and twigs. Sometimes the leaves are damaged by
leaf-spot fungi and various kinds of mildew.
Range
&
Habitat: The native American Holly is a rare tree in
Illinois,
occurring in only a single county in southern Illinois (see
Distribution
Map).
This tree is more common in southeastern United
States, particularly in sandy areas along the Atlantic coast. In
Illinois, American Holly has been found along a rocky wooded slope.
Outside of the state, it occurs in such habitats as well-drained areas
of bottomland woodlands, rocky upland woodlands, and sandy savannas.
These wooded areas often contain both coniferous trees (primarily
southern pines) and deciduous trees (oaks and miscellaneous others).
Because of its slow growth and tolerance of shade, American Holly is
often an understory tree in these habitats. Because of its thin bark,
it is easily killed by wildfires. Because of its ornamental qualities,
American Holly is often cultivated as a small- to medium-sized
landscape tree.
Faunal Associations: The nectar and pollen of
the flowers attract various insects, including bees, wasps, ants,
flies, and moths. While this tree was being photographed in an urban
park, the author of this website observed Spring Azure butterflies
(
Celastrina argiolus)
sucking nectar from the flowers. Other insects
feed more destructively on American Holly. These species
include caterpillars of the moth
Metaxaglaea
violacea
(Holly
Sallow), the fly larvae of
Phytomyza
ilicicola (Native Holly Leafminer)
and
Phytomyza ilicis
(Holly Leafminer), the fruit-eating larvae of
Asphondylia ilicicola
(Holly Midge), and
Asterolecanium
puteanum (Holly
Pit Scale). An arachnid invertebrate,
Oligonychus ilicis
(Southern Red
Mite), also feeds on American Holly, damaging the leaves and twigs. The
colorful and somewhat bitter fruit of American Holly is consumed
primarily by birds and, to a lesser extent, by some mammals. Birds that
eat the fruits include the Wild Turkey, Bobwhite, Northern Flicker,
Northern Mockingbird, and Cedar Waxwing; the
Bird Table provides
a more
complete listing of these species. Mammals that feed on the fruits
include the Raccoon, Striped Skunk, Fox Squirrel, Gray Squirrel, and
White-Footed Mouse. Because of their low palatability and mild
toxicity, the leafy branches are not preferred as a food source by
mammalian herbivores. However, when little else is available,
White-Tailed Deer and domesticated cattle occasionally browse on them.
Photographic Location: Crystal Lake Park in Urbana,
Illinois.
Comments:
American Holly is an interesting tree with attractive foliage and
fruit. Among evergreen broad-leaved trees, it is the most cold-hardy in
North America and can be grown north of its native range (if
appropriate cultivars are selected). Because of saponins and the bitter
compound ilicin, the fruit is not palatable to humans. Other species of
the Holly family in Illinois are deciduous-leaved shrubs that do not
attain the tree-like stature of American Holly; their deciduous leaves
are neither leathery nor spiny. A non-native species,
Ilex
aquifolium (English Holly) does resemble American Holly,
except it is
somewhat smaller in size and its evergreen leaves and fruit are more
shiny. While English Holly is occasionally cultivated, it does not
adapt well to a continental climate and it apparently has not
naturalized within the state.