Nepenthes angasanensis is a tropical pitcher plant species endemic to Sumatra, where it grows at an altitude of 1400m (4,600feet) to 3100m (10,200feet) above sea level.[1] The status of this taxon is controversial as it is similar in morphology to N. mikei and N. tobaica. It has even been suggested that the taxon might represent a natural hybrid between N. densiflora and N. tobaica.[2]
The specific epithet refers to Mount Puncak Angasan, from which the type specimen was collected. No forms or varieties of N. angasanensis have been described.
| Habit | Produces offshoots from underground rhizomes | No rhizomes | No rhizomes | |
| Spur | Forked | Fasciculate | Filiform | |
| Inner margin of peristome | Teeth to 1.5mm to 2mm long | Teeth to 0.2mm to 0.4mm long | Teeth < 0.2mm | |
| Stem cross section | Cylindrical | Cylindrical | Cylindrical to obtusely triangular | |
| Bracteoles | Sometimes near base of lowest pedicel only | Half way up every pedicel | At base or slightly below pedicel attachment, few | |
| Pitcher glands | 300 / cm2 (1900 per sq in) | 150–180 / cm2 (1000 to 1200 per sq in) | 200–250 / cm2 (1300 to 1600 per sq in) | |
| Pedicels | 1-flowered | 1-flowered | 2-flowered | |
| Inflorescence (female) | 5.5cm (02.2inches) to 12.5cm (04.9inches) long, 9–17 flowers | 4cm (02inches) to 8cm (03inches) long, 4–10 flowers | 19.5cm (07.7inches) to 40cm (20inches) long, 30–50 flowers |
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.[3]
The following natural hybrids involving N. angasanensis have been recorded.