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blackjack oak

blackjack oak (Quercus marilandica)
Photo © John Hilty

Features and Behaviors

The blackjack oak, also known as the scrub oak, is a deciduous tree that may grow to a height of 50 feet and a trunk diameter of one and one-half feet. The dark brown, shallowly ridged bark is divided into square blocks. The brown twigs are stout and hairy. The pith in the twigs is star-shaped when seen in cross-section. This tree’s simple, alternate leaves grow to about four to eight inches in length. Each long, leathery leaf is broader at the tip than at the base, with the broad end divided into three bristle-tipped lobes. The lower leaf surface is hairy. The leafstalk is less than one inch long. Staminate (male) and pistillate (female) flowers are found on the same tree. The male flowers are arranged in a catkin, while the female flowers are solitary or in groups of two or three. The fruit is an acorn, that has a nearly spherical shape. An average-sized acorn is slightly less than one-half inch in diameter. The cup encloses about one-half of the acorn.

Blackjack oak may be found in the southern two-thirds of Illinois. It grows in poor soil in upland woods and on bluffs. Flowers are produced in April and May. The fruits ripen in October of their second year. The dark brown wood is hard, strong and heavy and is used as a source of charcoal and fuel.

Illinois Range


​Kingdom: Plantae

Division: Magnoliophyta

Class: Magnoliopsida

Order: Fagales

Family: Fagaceae

Illinois Status

​common, native

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