There are few Illinois native oaks one might consider small or even medium in size, but blackjack oak fits the bill. Commonly found growing in poor soil, particularly xeric sandy or rocky sites throughout west-central into southern Illinois, Quercus marilandica is a slow-growing, long-lived species. Where it occurs in nature, it can appear “shrubby,” often killed back by fire and resprouting from the roots. This habit can be seen in trees in nearby Mason County, particularly at Sand Prairie-Scrub Oak Nature Preserve where blackjack oak is one of the primary components of the forested areas. In challenging conditions such as this, most trees range from 10’-30’ in height, though very old trees or those growing in richer soils can reach 50’ or more.
The leaves are unique to the species, widest at the apex where it ends with three to five shallow lobes with bristles. As with many plants suited to dry environments, the leaves are thick, leathery, and glossy. Deep green in summer, turn to a vibrant orange in fall, and often are marcescent in winter. They are very attractive in all seasons! It is not uncommon to encounter hybrids of this species with other red oaks. Quercus ×bushii is particularly common, a hybrid with Quercus velutina. Hybrids can vary greatly in appearance, but the telltale sign in this case is a leaf with more than the typical 3-5 lobes, with lobes deeper than you would expect to occur in a blackjack oak. You will find this hybrid, as well as the straight species and Quercus marilandica var. ashei, a western form identified by its diminutive leaves, in the collection at Starhill.
Thinking about planting a blackjack oak? They are not easy to find in the nursery trade, as plants known to be slow growers are not often prioritized, and the species has a reputation for being somewhat difficult to transplant if not grown with good root training techniques in the nursery. However, its medium size and adaptability to drought and heat make it an ideal tree for urban planting. If longevity, character, and species diversity are your goals, consider this tree!