B. L. Turner: The Comps of Mexico. A Systematic Account of the Family Asteraceae.
Chapter 18: Tribe Heliantheae [Part 1b]. Genera: Helianthus, Heliomeris, Hymenostephium, Iostephane, Lagascea, Sclerocarpus, Sidneya, Simsia, Tithonia, Viguiera
(Phytologia Memoirs Vol. 23b, 2015)