but it was recently found on a second mountain, where it grows at lower elevations of around 1600 m above sea level. On Mount Talakmau, the species occurs at an altitude of 1800–2700 m. At lower elevations on Talakmau, it grows epiphytically in montane forest. However, above around 2400 m, vegetation is very stunted and here N. dubia also grows terrestrially on clumps of moss. In its natural habitat, N. dubia is sympatric with N. gymnamphora, N. izumiae, N. jamban, and N. lingulata. The stunted upper montane forest which these species inhabit is dominated by ferns of the genera Dipteris and Dicranopteris. Trees rarely exceed 3 m in height and few Nepenthes plants emerge above the vegetation. Due to its extremely localised distribution, N. dubia is listed as Critically Endangered on the 2006 IUCN Red List of Threatened Species. N. dubia occurs at several locations along the only permanent trail up Mount Talakmau. However, the upper pitchers of this species bear a peristome, and so are not as desirable as those of N. inermis. Because of this, wild populations of N. dubia have not suffered from over-collection. Carnivory Nepenthes dubia produces thick, mucilaginous pitcher liquid similar to that found in related species such as N. inermis. The pitchers of N. inermis function not only as pitfall traps but also as flypaper traps, with the sticky inner walls trapping flying insects above the surface of the fluid. A similar trapping method may be employed by N. dubia. Nepenthes like N. jamban also use this method with mucilaginous pitcher fluid. Related species Nepenthes dubia belongs to a group of closely related montane Sumatran species that includes N. flava, N. inermis, N. jacquelineae, N. jamban, N. talangensis, and N. tenuis. These species are characterised by infundibular upper pitchers and highly viscous pitcher fluid. Nepenthes dubia is thought to be most closely related to N. inermis. It shares with this species the general morphology of its pitchers and leaves. It differs in having a well-developed peristome, more glands on the underside of the lid, and the lid being reflexed by more than 180 degrees. The lid of N. dubia is unique in this respect and is almost always reflexed beyond this angle, unless surrounding objects prevent it from assuming such a position. In their description of N. tenuis, Joachim Nerz and Andreas Wistuba included a table of morphological characteristics that distinguish it from related