"Nepenthes longifolia" was formally described by Joachim Nerz and Andreas Wistuba in a 1994 issue of the "Carnivorous Plant Newsletter". The holotype of "N. longifolia", "Nerz 2801", was collected by Joachim Nerz on September 25, 1992, in the Tjampo Mountains near Taram, West Sumatra, at an altitude of 1000 m. It is deposited at the National Herbarium of the Netherlands in Leiden. Seven other specimens of "N. longifolia" were collected on the same day and at the same location; "Nerz 2802", "2803", "2804", and "2805" are deposited at the National Herbarium of the Netherlands (L) together with the holotype, while "Nerz 2806", "2807", and "2808" are held at the Institut für Biologie I at the University of Tübingen (TUB) in Germany.