species, including N. dubia: In 2001, Charles 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 hybrids A single mature female plant of N. dubia × N. izumiae grows along the summit trail on Mount Talakmau. It produces infundibular upper pitchers that are yellowish-green in colouration. The pitchers are relatively small, reaching only around 10 cm in height. As in N. dubia, the stem and tendrils are purplish-red. The lamina is green with a red midrib. Nepenthes dubia × N. izumiae differs most obviously from N. dubia in having an ovate lid that is never reflexed beyond 180 degrees. This hybrid is listed as N. dubia × N. singalana in Charles Clarke's Nepenthes of Sumatra and Peninsular Malaysia, since N. izumiae is very closely related to N. singalana and was only described as a distinct species in 2003. In 2009, Adrian Y. Wartono observed a putative cross between N. dubia and N. jamban in an area where these two species grew with N. lingulata and N. rhombicaulis. Among natural populations of N. jacquelineae, botanist Andreas Wistuba observed a single plant that appears to represent a natural cross between N. dubia and N. jacquelineae. Notes a.Bünnemeijer reached the base of Mount Talakmau and set up camp there on April 21, 1917, at 400 m altitude. This was followed by a stay at 1060 m on the mountain's northwestern slope on May 6, at 1300 m on May 11, at 1900 m on May 21, and finally on the plateau, at an elevation of 2780 m, between June 1 and June 4, during which he climbed the summit. b.The original Latin description of N. dubia reads: Folia mediocria sessilia, lamina lanceolato-spathulata, nervis longitudinalibus utrinque c. 3, basi attenuata 1/3-2/3 caulis amplectente, vagina 0 ; ascidia rosularum et inferiora ignota ; ascidia superiora parva, parte inferiore tubulosa v. leviter ventricosa, supra medium infundibuliformia, costis 2 prominentibus ; peristomio fere horizontali, operculum versus acuto, applanato, 2-4 mm lato, costis 1/2-1/4 mm distantibus, dentibus 0 ; operculo anguste cuneato, facie inferiore plana ; inflorescentia ignota ; indumentum parcum, iuventute tomentum fuscum, denique deciduum. References Further reading Hernawati &