Nepenthes tenuis (; ) is a tropical pitcher plant endemic to the Indonesian island of Sumatra. The species was first collected in 1957, from a remote mountain in the western part of the island. It remained undescribed until 1994, and was only rediscovered in the wild in 2002. Prior to this, N. tenuis was known solely from a single photograph and dried herbarium specimen. Discovery and naming Nepenthes tenuis was first collected by Willem Meijer on August 24, 1957. It was discovered near Taram, West Sumatra, in a sandstone region of the river Tjampo. The plants were growing on a ridge at approximately 1000 m above sea level, making N. tenuis an intermediate species. The habitat was described as "light sub-montane forest". Nepenthes tenuis was formally described as a species in 1994 by Joachim Nerz and Andreas Wistuba, based on a single specimen deposited by Meijer at the Leiden herbarium and a black and white photograph from 1957 showing the freshly collected plant. After several failed expeditions, the species was finally rediscovered in the wild in late 2002 by a team comprising Andreas Wistuba, Joachim Nerz, Michael Schach, and others. Description Nepenthes tenuis is a climbing plant. The stem is slender (2–3 mm thick) and angular to rhomboid in cross section. Internodes are 5-6.5 cm long. Leaves are sessile and coriaceous. The lamina is lanceolate in morphology, 5–6 cm long, and 1-1.5 cm wide. It has an acute apex and is gradually attenuate towards the base, clasping the stem for two-thirds of its width (without a sheath). The lamina has indistinct nervation. Three or so longitudinal veins are present on either side of the midrib, originating from the basal third of the midrib and running parallel to it in the outer half of the lamina. Pinnate veins are oblique and irregularly reticulate, although they are not easily distinguishable. Tendrils are approximately 1.5 times as long as the lamina, growing to 12 cm in length and 0.5–1 mm in thickness. The tendrils may or may not curl around surrounding objects for support. Nepenthes tenuis is one of the smallest-pitchered species in the genus, possibly only second to N. argentii. Upper pitchers gradually arise from the ends of the tendrils, forming a 10 mm wide curve. They are widely infundibuliform (funnel-shaped) throughout and contracted below the mouth. These aerial pitchers are usually 2.5-4.5 cm high and 1.5-2.5 cm wide. Both lower and