Norrmann GA, Quarin CL, Keeler KH. Evolutionary implications of meiotic chromosome behavior, reproductive biology, and hybridization in 6X and 9X cytotypes of Andropogon gerardii (Poaceae ). American Journal of Botany. 1997;84:201 -207. Available at: http://www.amjbot.org/content/84/2/201.short.