Nepenthes rigidifolia is a critically endangered tropical pitcher plant endemic to Sumatra, where it grows at elevations of 1000–1600 m above sea level. The specific epithet rigidifolia is formed from the Latin words rigidus (rigid) and folia (leaves), and refers to the plant's stiff, coriaceous leaf blades. Tahul-tahul has been recorded as a local vernacular name for this species. Botanical history Nepenthes rigidifolia was discovered by Ch'ien Lee some time before 2001. The species was mentioned as an undescribed taxon in Charles Clarke's 2001 book, Nepenthes of Sumatra and Peninsular Malaysia, under the name "Nepenthes species A". At the time, it was recorded as growing at an elevation of around 1600 m. In 2004, Ch'ien Lee informally named the species N. alpicola and later N. aptera. Cultivated plants were sold under both of these names. Although intended to become scientific names, they were never published with an adequate description and are thus considered nomina nuda. Instead, the species was formally described later that year as N. rigidifolia by Pitra Akhriadi, Hernawati, and Rusjdi Tamin. The description was published on November 22, 2004. Two years later, Hernawati and Akhriadi covered the species in their book, A Field Guide to the Nepenthes of Sumatra, and assessed its conservation status. The holotype of N. rigidifolia—Nepenthes Team (Hernawati, P. Akhriadi & I. Petra) NP 354—was collected on December 11, 2003, near Sidikalang in Karo Regency, North Sumatra, at an elevation of 1000–1500 m. It is deposited at the Herbarium Universitas Andalas (ANDA) of Andalas University in Padang, West Sumatra. An isotype is held at Herbarium Bogoriense (BO) in Java. Stewart McPherson observed N. rigidifolia at the type locality in 2007 and published an updated description of the species in his 2009 monograph, Pitcher Plants of the Old World. Description Nepenthes rigidifolia is a climbing plant. The stem, which may be branched, is cylindrical and up to 1.3 cm in diameter. It can attain a length in excess of 10 m. Internodes are up to 5.1 cm long. Leaves are sessile to broadly sub-petiolate and have a coriaceous texture. They are noted for being particularly thick and rigid. The lamina is usually spathulate-oblong, but may also be ovate in rosettes. It reaches a maximum recorded length of 20.8 cm and width of 7.8 cm. It is gradually attenuate towards the base, clasping the stem for half to two-thirds of its circumference. The apex of the