Verbatim text: Clevenger, S. and C. B. Heiser. 1963. Helianthus laetiflorus and Helianthus rigidus—hybrids or species? Rhodora 65: 121–133.
Author: Clevenger, S., Heiser, C.B.
Year: 1963
Title: Helianthus laetiflorus and Helianthus rigidus—hybrids or species?
Journal: Rhodora
Volume: 65
Pages: 121–133