Nepenthes muluensis — Vorstman's Guide to the Carnivorous Plants

Nepenthes muluensis — the trap in close-up — **The trap in close-up** · Photo: JeremiahsCPs — CC BY-SA 3.0 · Wikimedia Commons

Nepenthes muluensis — the habitat — **The habitat** · Photo: JeremiahsCPs — CC BY-SA 3.0 · Wikimedia Commons

Identification

A climber with thin stems to 4 m long and 5 mm thick, with cylindrical internodes to 8 cm. The leaves are stalkless and leathery, lanceolate, to 8 cm long and only 1.5 cm wide, with an acute tip and a clasping base; the tendril reaches 8 cm. Lower pitchers are to 7 cm tall and 3 cm wide, ovoid in the lower third and cylindrical or conical above, with a round to ovate, obliquely set mouth and a cylindrical peristome of about 5 mm with small teeth. The ovate lid bears filiform appendages to 5 mm. Upper pitchers are cylindrical with an often bulbous base, to 10 cm tall and 2 cm wide, with ribs instead of wings, a round mouth, a peristome to 3 mm and a round lid without appendages. The plant is wholly hairless.

Similar species

The species is most easily confused with Nepenthes tentaculata, which occurs in the same area, often a little lower. The lower pitchers are nearly identical, but those of N. muluensis have a rounder mouth; the leaves are usually narrower. The best character is the upper pitcher: in N. muluensis with a white lid, a round mouth and greatly reduced or no wings, in N. tentaculata with an ovate lid that often bears filiform hairs. Like N. tentaculata, the species belongs to the Hamata group.

The trap and how it works

A small pitfall in two forms. Lower pitchers sit in the moss and, as in N. tentaculata, carry filiform appendages on the lid. Upper pitchers have a well-developed waxy zone on the inner wall, on which insects find no grip, and a white peristome and lid that contrast sharply with the dark purple pitcher; the contrast shows up well in the half-light of the mist and may serve as a lure. The digestive glands lie at the bottom. Little has been published on the prey; the plant's chemistry has been studied, however, showing that it lacks certain flavonoids and cyanidin found in N. tentaculata.

Habitat and ecology

Open places in mossy upper montane forest and ridge-top vegetation (B1), on nutrient-poor soils, between 1700 and 2400 m. On the summit of Gunung Mulu the vegetation is greatly stunted, rarely over a metre tall, and dominated by Rhododendron ericoides and species of Diplycosia and Vaccinium. On Mount Murud, populations grow in shaded mossy forest, and there the pitchers are darker. The plant climbs through the low shrubs with its thin stems.

Distribution and elevation

Endemic to Borneo. Known from Gunung Mulu, Gunung Api, Mount Murud and Bukit Batu Lawi in Sarawak, and from south-western Sabah. On Mulu it grows from about 1900 m to the summit at 2376 m. It is not known from the nearby summit of Benarat. Altitude: 1700 to 2400 m. Our species list names only Gunung Mulu; the species is now known from several mountains in Sarawak and from Sabah as well.

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 cells are 2 one-degree squares — 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: the locality of poached species is obscured at source. At this scale that obscuring disappears into the noise. The cells show where it has been seen, not where it occurs: an empty square means nothing.

Forms and variation

No varieties have been described. Populations do differ in colour: on Mulu the lower pitchers are dark purple with sparse yellow speckles and the upper pitchers purple with many yellowish-white speckles and a white peristome and lid; on Murud the pitchers are darker, possibly because of stronger ultraviolet at higher altitude. Two natural hybrids have been reported: with N. lowii, and with N. tentaculata, described in 1993 as N. ×sarawakiensis; the existence of the latter is doubted.

Where and when to see it

The climb to the summit of Gunung Mulu is a trek of several days within the national park, only with a park guide and after booking with the park administration. Above about 1900 m, in the low scrub on the ridge, the dark purple pitchers with their white lids can be found among moss and rhododendrons. The plants are small; look low and carefully. Collecting plants is prohibited in the park.

Conservation status

The Red List assesses the species as Least Concern (2018 assessment). Earlier assessments were stricter: Endangered in 1995 and Vulnerable in 2000, and Clarke in 1997 called it endangered but conservation dependent. The shift mainly reflects the finds on other mountains. The Mulu populations lie in a national park and World Heritage Site. The species is listed in CITES Appendix II.

Scientific name

Nepenthes muluensis | Hotta, 1966

Nepenthes muluensis was described in 1966 by Mitsuru Hotta, in "Notes on Bornean plants" (Acta Phytotaxonomica et Geobotanica). The holotype (M. Hotta 14791d) was collected on 18 March 1964 on the Mardi route, between the third and fourth camps on the western ridge of Mount Mulu, Sarawak, and is held at the Botany Department of Kyoto University. The western ridge of Mount Mulu, between the third and fourth camps on the Mardi route, Sarawak, Borneo. The species is named after Mount Mulu, to which it was thought to be endemic.

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