Quercus marilandica (Blackjack oak) is a small oak, one of the red oak group Quercus sect. Lobatae, but fairly isolated from the others. It is native to the southern and central United States, with populations following the eastern seaboard north to Long Island.

It is a small deciduous tree growing to 15 m tall, with bark cracked into rectangular black plates with narrow orange fissures. The leaves are 7-20 cm long and broad, and typically flare from a tapered base to a broad three-lobed bell shape with only shallow indentations. They are dark green and glossy above, pubescent underneath, and often remain attached to the twigs through the winter after turning colors from red to brown in the fall. The acorn is small, 12-20 mm long and 10-18 mm broad; like other red oaks, it takes 18 months to mature.