Roland McMillan Harper, older brother of Francis Harper, was also a botanist and naturalist. He studied engineering in his undergraduate education and later received a doctorate in 1905 from Columbia University, focused on his work with the flora of Georgia.

From 1905-1906 he was botanist and geographer for the Alabama Geographical Society. He then held similar roles for the American Museum of Natural History, U.S. National Herbarium, U.S. Department of Agriculture, the Biltmore Forest School, and for the Arnold Arboretum.

Roland Harper discovered 30 new flowering plant species throughout the American Southwest and Mid-Atlantic coast, particularly in Florida, Georgia, Arkansas, and New York. He accompanied his brother Francis in retracing William Bartram's journey.

Roland Harper married Mary Susan Wigley at the age of 65, in 1943. He died in 1966.