Nuttall, T. 1840. Descriptions of new species and genera of plants in the natural order of the Compositae, collected in a tour across the continent to the Pacific, a residence in Oregon, and a visit to the Sandwich Islands and upper California, during the years 1834 and 1835. Transactions of the American Philosophical Society, held at Philadelphia, for promoting useful knowledge, n.s.[new series][ser. 2], 7: 283–453. BHLReference page.