Howard, Elizabeth; Aschen, Harlen; Davis, Andrew K. (2010). "Citizen Science Observations of Monarch Butterfly Overwintering in the Southern United States". Psyche: A Journal of Entomology2010: 1–6. doi:10.1155/2010/689301.
Singh, B.; Rastogi, R.P. (February 1972). "Structure of asclepin and some observations on the NMR spectra of Calotropis glycosides". Phytochemistry11 (2): 757–762. doi:10.1016/0031-9422(72)80044-X.