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Thomas Nuttall, Descriptions of New Species and Genera of Plants in the Natural Order of the Compositæ, 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, Vol. 7 (1841), pp. 283-453
Thomas Nuttall (Fri,) studied this question.