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Nepenthes pilosa
A hairy mountain species from the heart of Borneo with a curious history: described in 1928 and then confused with another plant for almost a century. Nepenthes pilosa was collected in 1899 by the Javanese plant collector Amdjah, who travelled with Nieuwenhuis's expedition across central Borneo. Danser described it in 1928 in his great monograph of the pitcher plants of the Netherlands Indies. Only when Charles Clarke visited the type locality in 2004 and 2006 did it emerge that virtually everything known under this name in the meantime belonged to another species, since called Nepenthes chaniana. The true pilosa is a rare plant of a single mountain area.
Identification
A climber with a stem to about seven metres long. The leaves are lanceolate, to 30 cm long and 7.5 cm wide, with four to five veins on either side of the midrib. The indumentum is striking: young parts and the undersides of the leaves are densely covered in yellow-brown hairs, while the upper leaf surface stays glabrous. The lower pitchers are small, ovate and cylindrical above, to 10 cm tall, with a flattened peristome to 7 mm wide. The upper pitchers are funnel-shaped, to 18 cm tall and 8 cm wide, with a wider peristome to 12 mm. The key character sits under the lid: in the upper pitchers it bears a conspicuous hooked appendage near its base.
Similar species
The species most confused with N. pilosa is Nepenthes chaniana of Sabah and Sarawak. Both are hairy and have a hooked appendage under the lid. The pitchers of N. pilosa, however, are squatter, more cylindrical and rounder, and not as laterally compressed as the long, narrow pitchers of N. chaniana. Nepenthes burbidgeae of Kinabalu has a similar lid appendage but is far less hairy. Within Borneo these are the only three species with such a hooked appendage, and all are placed in the N. maxima complex.
The trap and how it works
The pitchers work as pitfalls. Nectar on the peristome and under the lid lures insects; when the peristome is wet they lose their footing on the slippery ribs and fall into the fluid below, where glands secrete digestive enzymes and absorb nutrients. Danser counted six to seven hundred glands per square centimetre in the lower pitchers and two to two and a half thousand in the upper ones. The lower pitchers stand in moss and take mainly walking animals; the upper pitchers hang in the vegetation. Nothing has been published on the prey of this species. The pitcher fluid of many Nepenthes species also holds a small community of its own, of mosquito larvae, mites and other animals living off the captured prey; whether this is also true of this species has not been studied.
Habitat and ecology
Mossy mountain forest, cloud forest at about 1600 to 1700 m (B1). The soil is acid and poor, the forest low and permanently damp, with thick layers of moss on trunks and branches. The plant climbs from the moss on the ground into the trees. At Clarke's visit the population was estimated at about two hundred plants; little else is known of its ecology.
Distribution and elevation
Endemic to Borneo and, as far as is known, confined to the mountain area of Bukit Batu Lesung in East Kalimantan, in the interior of the island. A herbarium specimen from 1925 from a neighbouring mountain is doubtful. The guide's own species list gives simply 'Borneo'; that is correct, but the real range is far smaller than the label suggests. Older records from Sabah and Sarawak, including those in Flora Malesiana, refer to N. chaniana.
- Recorded (one-degree cells)
Forms and variation
No varieties or colour forms have been described, and given the small number of known plants little is known about variation. No natural hybrids have been established: crosses with Nepenthes lowii and Nepenthes veitchii mentioned in older literature turn out to refer to N. chaniana or to rest on misidentification. Cultivated material circulating as pilosa is almost always N. chaniana.
Where and when to see it
In practice this species is out of reach for almost everyone: the mountain area lies deep in the interior of Kalimantan, without roads, and getting there takes an expedition of several days with local guides. Anyone who does go would do well to study Clarke's account, so as not to take the plant for another hairy species, and to keep localities private. With so small a population, every disturbance counts.
Conservation status
On the Red List N. pilosa is Data Deficient (assessed 2014), so no full risk assessment has proved possible. What is known: the species is recorded from a single mountain area, the population is small, and the area is remote, which probably protects the plants from collectors but also hampers research. Fire and clearance in the Kalimantan lowlands do not directly affect the cloud forest, but its surroundings are changing fast. Like the whole genus it is listed in CITES Appendix II.
Scientific name
Nepenthes pilosa | Danser, 1928
Nepenthes pilosa was described in 1928 by Benedictus Hubertus Danser, in his monograph "The Nepenthaceae of the Netherlands Indies" (Bulletin du Jardin Botanique de Buitenzorg). The type material (Amdjah 491) was collected on 28 January 1899 on Mount Bukit Batu Lesung, near the centre of Kalimantan, at approximately 1,600 m elevation, by the Javanese plant collector Amdjah, during the Nieuwenhuis Expedition. Bukit Batu Lesung, near the centre of Kalimantan, Borneo, at approximately 1,600 m elevation — the same mountain as N. ephippiata (golf 21). The specific epithet derives from the Latin "pilosus" ("hairy"), referring to the plant's dense indumentum of long yellow-brown hairs.
World Checklist of Vascular Plants (WCVP), via Plants of the World Online (POWO), Royal Botanic Gardens, Kew.