In 1840, when Eliza Steele marveled at being surrounded by a vast prairie of grass and flowers, Illinois had approximately 22,000,000 acres of prairie, but today fewer than 2,500 acres of high quality prairie remain. Prairies are dominated by grasses and wildflowers, with trees absent or scarce, and in Illinois their types are distinguished by topography and soil as black soil, hill, shrub, dolomite, sand, and gravel prairies. Most Illinois prairies are tallgrass prairies, where plant types vary with the amount of available moisture. The Illinois Department of Natural Resources, aided by other groups around the state, works to preserve, maintain, and restore prairie environments, including periodic burning to prevent trees from taking over, since prairie plants are adapted to grow back after fire. Common Illinois prairie plants include prairie blazing star, which flowers in August and September; big bluestem, the tallest and most widely distributed prairie grass in Illinois; black-eyed Susan, common on hill prairies and blooming from mid-spring through fall; pale purple coneflower, whose flowers appear in June and bloom through July and whose roots were used in herbal medicines; eastern prickly pear, common in sandy prairie soils and eaten by the eastern box turtle; and rattlesnake master, found in most prairies and used by Native Americans in medicine and as an antidote for snake bites.