Alternate deciduous leaves occur along twigs and young shoots; because they are often bunched together, the leaves may appear opposite or whorled. Leaf blades are 2½-6" long and deeply pinnatifid with 5-7 bristle-tipped lobes. The lobes taper to narrow points and they are separated by wide concave sinuses. The upper blade surface is medium to dark green, hairless, and shiny, while the lower blade surface is pale green and largely hairless, except for tufts of hair at the junctions of major veins. The slender petioles are light green or yellowish green, hairless, and shiny; they are ¾-2½" long. Pin Oak is monoecious, producing separate male (staminate) and female (pistillate) flowers on the same tree when the leaves emerge during the spring. Male flowers are produced on twigs of the preceding year in the form of drooping catkins; they are yellowish green and about 1½-4" long. Female flowers are produced on leafy shoots of the current year in the form of short spikes less than ¾" long; there are 1-4 female flowers per spike. Each male flower has several stamens, while each female flower has an ovary with 3 stigmata.
The blooming period occurs during mid- to late spring for about 1-2 weeks; flowers are cross-pollinated by the wind. Fertile female flowers are replaced by acorns that take two years to develop; they mature during autumn of the second year. Mature acorns are about 1/3-1/2" (8-12 mm.) long and similarly across; each acorn is globoid or subgloboid in shape with a shallow cap that extends downward to about one-fourth the length of the acorn. The small scales of the cap are overlapping and appressed. The body of a mature acorn is medium brown to nearly black, often with narrow vertical lines along its sides; the apex of the body underneath the cap is tan. The cap of a mature acorn is light brown to reddish brown and either glabrous or sparsely canescent. The woody root system has numerous lateral roots that are shallow and spreading. The leaves of Pin Oak become yellow, red, or brown during the autumn; they sometimes persist on the branches of this tree during the winter.
Cultivation: The preference is full sun, moist well-drained conditions, and a somewhat acidic soil that contains sand, clay, or loam. Flooded conditions are tolerated during winter and early spring dormancy, but not during the period of active growth. Partial sun is also tolerated, but it may cause die-back of some branches. Because it lacks a deep taproot, Pin Oak transplants more easily than most oaks. It also grows faster than most oaks. Longevity of a healthy tree is typically 100-150 years. Pin Oak is vulnerable to oak wilt disease, which can be fatal.
Range & Habitat: Pin Oak is occasional to locally common in the southern half of Illinois, becoming less common or absent in parts of northern Illinois. Habitats consist of floodplain woodlands, flatwoods in upland areas, poorly drained areas of sandy woodlands, gravelly acidic seeps in wooded areas, and higher ground in swamps. These habitats often have a layer of clay subsoil that inhibits drainage; Pin Oak also occurs in habitats with moist sandy soil. Because of the relatively thin bark, its tolerance to wildfires is poor.
Faunal Associations: Many insects feed on the foliage, bore through the wood, suck plant juices, etc., of Pin Oak and other oaks. The caterpillars of several Hairstreak butterflies and Duskywing skippers feed on the foliage of oaks; this includes Calycopis cecrops (Red-Banded Hairstreak), Fixsenia favonius ontario (Northern Hairstreak), Parrhasius m-album (White-M Hairstreak), Satyrium calanus falacer (Banded Hairstreak), Satyrium edwardsii (Edward's Hairstreak), Satyrium liparops strigosum (Striped Hairstreak), Erynnis brizo (Sleepy Duskywing), and Erynnis juvenalis (Juvenal's Duskywing). The caterpillars of Edward's Hairstreak use only species of the Red Oak group as a food source, of which Pin Oak is a member. The caterpillars of numerous moths feed on oaks; this includes such species as Anisota stigma (Spiny Oakworm), Lochmaeus manteo (Variable Oakleaf Caterpillar), Symmerista canicosta (Red-Humped Oakworm), and Valentina glandulella (Acorn Moth). The Moth Table provides a more complete list of these species. The larvae of Buprestids, long-horned beetles, and other beetles bore through the wood or bark of oaks (see Wood-Boring Beetle Table). Leaf beetles that feed on the foliage include Metachroma laevicolle and other Metachroma spp., Pachybrachis dilatatus and Pachybrachis morosus, and Paria opacicollis; this last species is a flea beetle. Oaks are hosts to many small insects that suck plant juices, especially treehoppers (mostly Cyrtolobus spp. & Telamona spp.). Other insects in this group include Myzocallis ahlhambra (Dusky-Winged Oak Aphid) and other aphids, Eratoneura richardsi and other leafhoppers, and Melanaspis obscura (Obscure Scale).
Another interesting group of insects are gall wasps, which often form various kinds of galls on the leaves or twigs of oaks. Some examples of species in this group include Amphibolips confluenta (Large Oak Apple Gall Wasp), Callirhytis cornigera (Horned Oak Gall Wasp), and Callirhytis quercuspunctata (Gouty Gall Wasp). The Insect Table provides a more complete list of species that feed on oaks. Because the Pin Oak has small acorns, they are especially valuable to birds as a food source; these acorn-eating birds include the Wood Duck, Mallard, Wild Turkey, Monk Parakeet (in Chicago & other urban areas), White-Breasted Nuthatch, Blue Jay, and Tufted Titmouse. Such mammals as the Fox Squirrel, Gray Squirrel, Red Squirrel, Southern Flying Squirrel, White-Footed Mouse, and even the Muskrat also eat the acorns. White-Tailed Deer occasionally browse on leaves and twigs of oaks. Oak trees provide nesting habitat for such birds as the Summer Tanager, Blue-Gray Gnatcatcher, Northern Parula, Yellow-Throated Vireo, and Swainson's Hawk. The Pin Oak, in particular, provides nesting habitat for herons, egrets, and other wetland birds that nest in colonies on trees, as this oak is often near bodies of water.
Photographic Location: The Arboretum of the University of Illinois and Crystal Lake Park in Urbana, Illinois.
Comments: Pin Oak is a member of the Red Oak group. Oak trees in this group have leaves with bristle-tipped lobes and bitter-tasting acorns that take 2 years to mature. Pin Oak can be distinguished from other oaks in this group by its deeply lobed leaves, small acorns (½" or less) with shallow cups, and drooping lower branches. Its bark is typically less furrowed and scaly than the bark of many other oaks. Pin Oak is often cultivated because of its tidy habit of growth, ornamental qualities, and the reduced ground litter that results from having small acorns and storm-resistant branches. Even though this tree is typically found in or around wetland areas, it readily adapts to drier sites in residential areas and urban parks.