morphology from these species and is not easily confused with them. In 1997, Matthew Jebb and Martin Cheek published their monograph "A skeletal revision of Nepenthes (Nepenthaceae)", in which they referred to N. dubia specimens from Mount Talang (Kurata s.n. SING) and the mountains of the Tjampo region near Payakumbuh (Meijer 6949 L). The latter specimen is the holotype of N. tenuis, which Jebb and Cheek treated in synonymy with N. dubia. However, subsequent authors have rejected this interpretation. Charles Clarke restored N. tenuis to species rank in Nepenthes of Sumatra and Peninsular Malaysia (2001), citing differences in pitcher morphology. Clarke also identified Kurata s.n. as the natural hybrid N. × pyriformis, which is similar to N. dubia, but can be distinguished on the basis of several stable characters. The hybrid has a wider pitcher lid that is never relfexed beyond 90 degrees and the pitcher cup is not appressed in the lower parts as in N. dubia. In addition, the mouth of N. × pyriformis is raised towards the back as opposed to being horizontal. Description Nepenthes dubia is a climbing plant. The stem can reach 3 m in length and is 3 to 4 mm in diameter. It is cylindrical or slightly angular. Internodes are up to 10 cm long. Leaves are sessile and coriaceous. The lamina is lanceolate-spathulate in form. It may be up to 10 cm long and 2 cm wide. It has an acute apex and is gradually attenuate towards the base, which clasps the stem for one third to a half of its circumference. Around three pairs of longitudinal veins are present on the lamina, originating from the basal third of the midrib. Pinnate veins are oblique and irregularly reticulate, although they are not easily distinguishable. Tendrils can be up to 15 cm long and may or may not have a curl. Rosette and lower pitchers are rarely produced. They are narrowly infundibular in the lower two-thirds, becoming ovoid above, and are sharply contracted below the rim. Terrestrial pitchers are relatively small, reaching 5 cm in height and 3.5 cm in width. A pair of fringed wings (≤3 mm wide) runs down the upper third of the pitcher beneath the rim. The glandular region covers the lower two-thirds of the inner surface. The pitcher mouth is round and slightly raised at the back. The peristome is cylindrical, up to 3 mm wide, and bears