species, Nerz and Wistuba included a table of "characteristics which clearly distinguish Nepenthes tenuis from similar species": Charles Clarke writes that "the obvious similarities between N. tenuis, N. talangensis and N. jacquelineae are suggestive of recent adaptive radiation, and add further weight to the argument that the non-volcanic mountains of Bukit Barisan are the primary source of morphological diversity in Sumatran Nepenthes". In 2001, Clarke performed a cladistic analysis of the Nepenthes species of Sumatra and Peninsular Malaysia using 70 morphological characteristics of each taxon. The following is part of the resultant cladogram, showing "Clade 1", which has 51% bootstrap support. Its most strongly supported subclade is the sister pair of N. inermis and N. dubia, having 95% support. Natural habitat and distribution Nepenthes tenuis grows in mossy forest and light sub-montane forest at the tops of sandstone ridges. The only known population occurs at an elevation of 1000–1200 m above sea level. Nepenthes tenuis is endemic to a region of the Tjampo river east of Taram in West Sumatra. Most ridges in this area have an elevation of just below 1000 m, although several exceed this height. Terrestrial pitchers of N. tenuis often develop partially embedded in moss. The lower parts of the stem may also be covered under a layer of moss, making the plants difficult to find in the wild. In its natural habitat, the species is sympatric with N. adnata and grows in close proximity to N. albomarginata, N. ampullaria, N. eustachya, N. gracilis, N. longifolia, and N. reinwardtiana. Despite this, no natural hybrids involving N. tenuis have been recorded. Nepenthes tenuis is listed as Endangered on the 2014 IUCN Red List of Threatened Species. The habitat of this species may be threatened in the near future by fires deliberately started to clear forest for agricultural purposes. Notes a.Meijer explored the forest of the Tjampo region between August 20 and August 28. He collected N. tenuis on August 24 together with the type material of N. adnata and the first known specimen of N. longifolia. b.The original Latin description reads: Planta tenuis. Folia mediocria sessilia lamina lanceolata, nervis longitudinalibus utrinque 3, basi attenuata 2/3 caulis amplectente. Vagina 0. Ascidia rosularum et inferiora ignota. Ascidia superiora parva, infundibuliformia, costis 2 elevatis; peristimio operculum versus accuminato in collum breve elevato, 6 mm lato, costis 1/8 mm distantibus; operculo anguste elliptico, facie inferiore piano. Inflorescentia ignota. c.The holotype of