E.  Hultén, ?The provenience of Artemisia verlotorum Lamotte?, Svensk Bot. Tidskr, vol. 23, pp. 496 - 505, 1929.

E. E.  Watson, ?Contributions to a monograph of the genus Helianthus?, Pap. Michigan Acad. Sc, vol. 9, pp. 305 - 475, 1929.