Nepenthes gracilis (from Latin: gracilis = thin, slender), or the Slender Pitcher-Plant, is a very common lowland pitcher plant that is widespread in the Sunda region. The pitchers are relatively unremarkable with a very thin peristome and no unusual morphological features. Despite being a widespread plant, natural hybrids between N. gracilis and other species are quite rare.
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 a portion of the resultant cladogram, showing part of "Clade 6". The sister pair of N. angasanensis and N. mikei has 79% support.
Despite varying little across its range, N. gracilis has a number of infraspecific taxa. Most of these are no longer considered valid.
- Nepenthes gracilis f. angustifolia (Mast.) Hort.Westphal (1993)
- Nepenthes gracilis var. angustifolia (Mast.) Hort.Weiner in sched. (1985)
- Nepenthes gracilis var. arenaria Ridl. ex Macf. (1908)
- Nepenthes gracilis var. elongata Bl. (1852)
- Nepenthes gracilis var. longinodis G.Beck (1895)
- Nepenthes gracilis var. major Hort.Lindsay ex Dixon (1889)
- Nepenthes gracilis var. teysmanniana (Miq.) Beck (1895)
The following natural hybrids involving N. gracilis have been recorded.
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- Normawati, Y. 2002. The effect of stem length on pitcher and inflorescence production in Nepenthes gracilis and Nepenthes mirabilis at Serendah Selangor. B.Sc. Thesis. Universiti Kebangsaan Malaysia.