m above sea level. At one location, N. glabrata has been found growing alongside N. maxima and Drosera burmannii at 1600 m. A putative natural hybrid with the former has been recorded. Nepenthes glabrata is classified as Least concern on the IUCN Red List of Threatened Species, based on an assessment carried out in 2015. Related species Nepenthes glabrata belongs to what has been called the "N. tentaculata group" or "Hamata group", which also includes four other closely related species from Borneo and Sulawesi: N. hamata, N. muluensis, N. murudensis, and N. tentaculata. More recently, N. nigra has joined this group of related taxa. In their 2001 monograph, Cheek and Jebb considered N. glabrata to be most closely allied to N. muluensis based on its atypical lid nervation as well as the size, shape, and pigmentation of its upper pitchers. Currently, it appears that N. glabrata is most closely related to N. pitopangii, a highland species also endemic to Sulawesi. While the stem, laminae, and lower pitchers of these species are very similar, the markedly different upper pitcher morphology means that they are unlikely to be confused. The aerial pitchers of N. pitopangii are far less elongated than those of N. glabrata and completely lack wings. Natural hybrids Where their ranges overlap, N. glabrata is known to hybridise with N. hamata, N. maxima, N. nigra, and N. tentaculata. The hybrid plants are generally intermediate in appearance between their parent species. References Further reading Bauer, U., C.J. Clemente, T. Renner & W. Federle 2012. Form follows function: morphological diversification and alternative trapping strategies in carnivorous Nepenthes pitcher plants. Journal of Evolutionary Biology 25(1): 90–102. Bonhomme, V., H. Pelloux-Prayer, E. Jousselin, Y. Forterre, J.-J. Labat & L. Gaume 2011. Slippery or sticky? Functional diversity in the trapping strategy of Nepenthes carnivorous plants. New Phytologist 191(2): 545–554. Darma, I.D.P., I.P. Suendra & H.-M. Siregar 2004. BP-17: Keanekaragaman Nepenthes di Taman Wisata Alam Nanggala III, Luwu, Sulawesi Selatan. [Nepenthes diversity in Taman Wisata Alam Nanggala III, Luwu, Sulawesi Selatan.] [pp. xiv–xv] In: Abstrak: Konggres dan Seminar Nasional Penggalang Taksonomi Tumbuhan Indonesia (PTTI) Universitas Sebelas Maret Surakarta, 19-20 Desember 2003. Sisipan Biodiversitas 5(1): i–xxxii. Darma, I.D.P., I.P. Suendra & H.-M. Siregar 2004. Keanekaragaman Nepenthes di Taman Wisata Alam Nanggala III, Luwu, Sulawesi Selatan. [Diversity of Nepenthes at ecotour forest Nanggala III, Luwu, South Sulawesi.] BioSMART 6(2): 126–129. Mansur, M. 2001. In: Prosiding Seminar Hari Cinta