Nepenthes aenigma — Vorstman's Guide to the Carnivorous Plants

No photograph of this species under a Creative Commons licence or in the public domain is in the guide yet.

Identification

A climber with stems up to five metres long and five to six millimetres thick, green to dark reddish. The leaves are sessile, linear to sword-shaped, to 19 cm long and 5.4 cm wide, with three or four longitudinal nerves on each side. The growth habit is peculiar: short stems at ground level produce pitchers lying in the litter, while older stems send up new aerial shoots from dormant buds that grow quickly. Intermediate pitchers are barrel-shaped to cylindrical, 11.7 to 15.9 cm tall and 4 to 6 cm wide, with two broad wings bearing branched fringes, a round, oblique mouth and a rounded peristome of seven to eight millimetres. They are pale green with elongated dark red spots, densest under the lid, and the peristome is cream to reddish. Upper pitchers are smaller, 7 to 11 cm, cylindrical and slightly curved, wholly green, with a flattened peristome and narrower wings that stop two-thirds to seven-eighths of the way down. True lower pitchers from a rosette have not been described.

Similar species

The nearest species in the area is Nepenthes ventricosa, which grows on the same mountains but at a different altitude. Nepenthes ventricosa has pitchers with a pronounced waist, like an hourglass, and inflorescences in which each side branch bears one flower. Nepenthes aenigma has cylindrical, winged pitchers that differ clearly between intermediate and upper, linear to elliptic leaves, and side branches mostly bearing two flowers. Outside Ilocos Norte there are no other species it might be confused with in the field.

The trap and how it works

A pitfall that here works largely on the ground. The intermediate pitchers lie in the leaf litter, where their wings with branched fringes serve as a walkway; the rounded, ribbed peristome, with ribs half a millimetre high and small teeth on the inner edge, turns slippery when wet. The lid carries elongated nectar glands in a V-shaped pattern. The authors examined pitcher contents: mainly ants, also spiders and cockroaches, and mosquito larvae lived in the fluid. That fits a trap lying in the shade on the forest floor, where walking animals are the main prey.

Habitat and ecology

Terrestrial in leaf litter, around 1200 m, in deep shade in windswept ravines with dense bamboo, rattan and screw pines (Pandanus). Remarkably, there is no mossy cloud forest at this altitude, and the species seeks out precisely the darkest places, where most pitcher plants would fail. The coded habitat (B1) is therefore an approximation: it is montane forest, but not of the classic mossy type.

Distribution and elevation

Endemic to Ilocos Norte province in north-western Luzon, where the authors knew three sites on two mountains about ten kilometres apart, all at around 1200 m. The label 'North Luzon' in our species list can thus be narrowed to Ilocos Norte. Herbarium data name the municipality of Pagudpud at the northern tip of the island.

Recorded (one-degree cells)

Distribution based solely on records at GBIF (Global Biodiversity Information Facility), not on TDWG regions — those are often far larger than the actual range. The light halo is the area around a record, the dark core the record itself. The darker square is the only one-degree cell — roughly a hundred and ten kilometres — in which the species has been recorded, from all GBIF records. This is coarser than for most species because hardly any record of this plant carries an accurate coordinate. It shows where the species has been seen, not where it occurs: an empty square means nothing.

Forms and variation

No varieties have been described. The colour difference between the intermediate pitchers, pale green with dark red spots, and the wholly green upper pitchers is large within one plant and should not be mistaken for variation between plants. No natural hybrids with Nepenthes ventricosa have been reported; the two species are separated by altitude.

Where and when to see it

This species is not in the open, sunny places where pitcher plants are usually sought. Search shady, windswept ravines around 1200 m, among bamboo and rattan, and look at the ground: the spotted intermediate pitchers lie in the litter and hardly stand out. The known populations are very small; tread carefully and leave everything as it is.

Conservation status

The species has not yet been assessed by the IUCN (Not Evaluated). The authors considered Critically Endangered on account of the low numbers, but finally proposed Data Deficient pending population studies. At the first site they counted only five plants in 2013, all male and with no seedlings, and the two other populations are also very small. There was no evidence of poaching or habitat disturbance. Like all Nepenthes the species is listed in CITES Appendix II.

Scientific name

Nepenthes aenigma | Nuytemans, Suarez & Calaramo, 2016

Described by Nuytemans, W. Suarez and Calaramo in 2016 (in Gronemeyer et al.), in Plants 5(2): 23. The plant had already been discovered in April 2002 by ornithologist Herman Nuytemans, but remained known for over a decade under the provisional name "Nepenthes sp. Luzon" before being formally described. The type locality lies on two mountains in Ilocos Norte province, on the island of Luzon, Philippines, at approximately 1200 metres altitude. The name "aenigma" is Latin for "riddle" and refers to this species' very unusual ecological preferences, thriving in deep shade — something that puzzled researchers at the time.

World Checklist of Vascular Plants (WCVP), via Plants of the World Online (POWO), Royal Botanic Gardens, Kew.