It has been suggested that N. negros might fall within the natural variability of N. ramos, though field studies would be needed to confirm this.[9]
^ abcdefCheek, M. & M. Jebb (2013). Typification and redelimitation of Nepenthes alata with notes on the N. alata group, and N. negros sp. nov. from the Philippines. Nordic Journal of Botany31(5): 616–622. doi:10.1111/j.1756-1051.2012.00099.x
^Schlauer, J. (N.d.). Nepenthes alata. Carnivorous Plant Database.
^Macfarlane, J.M. (1908). Nepenthaceae. In: A. Engler. Das Pflanzenreich IV, III, Heft 36: 1–91.
^ abCheek, M. & M. Jebb (2013). Nepenthes ramos (Nepenthaceae), a new species from Mindanao, Philippines. Willdenowia43(1): 107–111. doi:10.3372/wi.43.43112
^ abCheek, M. & M. Jebb (2013). Recircumscription of the Nepenthes alata group (Caryophyllales: Nepenthaceae), in the Philippines, with four new species. European Journal of Taxonomy69: 1–23. doi:10.5852/ejt.2013.69
^Cheek, M. & M. Jebb (2013). Nepenthes ultra (Nepenthaceae), a new species from Luzon, Philippines. Blumea, published online on October 24, 2013. doi:10.3767/000651913X675124
^Gronemeyer, T., W. Suarez, H. Nuytemans, M. Calaramo, A. Wistuba, F.S. Mey & V.B. Amoroso (2016). Two new Nepenthes species from the Philippines and an emended description of Nepenthes ramos. Plants5(2): 23. doi:10.3390/plants5020023