We have information from several sources:
The American Mayapple and its Potential for Podophyllotoxin Production —Rita M. Moraes, Hemant Lata, Ebru Bedir, Muhammad Maqbool, and Kent Cushman
Propagule Type and Planting Time for Field-established Mayapple—Muhammad Maqbool, Kent E. Cushman, and Rita M. Moraes
Assessment of Genetic Diversity in Podophyllum peltatum by Molecular Markers—Hemant Lata, Rita M. Moraes, Andrew Douglas, and Brian E. Scheffler
Bioprospecting for Podophyllotoxin—Ebru Bedir, Ikhlas Khan, Rita M. Moraes
Sievers, A.F. 1930. The Herb Hunters Guide. Misc. Publ. No. 77. USDA, Washington DC.