R. E.  Perdue, Jr., ?Two New Varieties and a New Combination in Rudbeckia?, Rhodora Journal of the New England Botanical Club, vol. 64, pp. 328-329, 1962.

R. E.  Perdue, Jr., ?Synopsis of Rudbeckia Subgenus Rudbeckia?, Rhodora Journal of the New England Botanical Club, vol. 59, 1957.