@article {8251,
	title = {Helianthus laetiflorus and Helianthus rigidus _ hybrids or species},
	journal = {Rhodora},
	volume = {65},
	year = {1963},
	month = {1963///},
	pages = {121 - 133},
	author = {S. Clevenger and C.B. Heiser}
}
@article {8047,
	title = {The North American sunflowers (Helianthus)},
	journal = {Mem. Torrey Bot. Club},
	volume = {22},
	year = {1969},
	month = {1969///},
	pages = {1 - 218},
	author = {C.B. Heiser and D.M. Smith and S. Clevenger and W.C. Martin}
}
