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Nepenthes robcantleyi
One of the most discussed pitcher plants of recent decades, and a species described from a plant in a glasshouse. In January 1997 the nurseryman Robert Cantley found two mature plants with enormous, almost black pitchers on a remote mountain on Mindanao, inside a logging concession. He collected seed; shortly afterwards the forest was cleared, and two searches in the following years found nothing more. Eleven plants grew from that seed, and it was from one of them that Martin Cheek described the species in 2011.
Identification
A robust, non-climbing shrub half a metre to a metre tall, with a stem about two centimetres thick and very large, thickly leathery leaves: the blade is oblong-elliptic and to over 28 cm long and almost as wide, on a petiole to 23 cm. The pitchers described for the species are intermediate pitchers about 33 cm tall and 9.5 cm wide, broadly cylindrical, with two broad fringed wings down the front. The most striking part is the peristome: about two centimetres wide at the front but flaring towards the back to five to ten centimetres, with high, wing-like ribs and teeth three to four millimetres long on the inner margin. The lid is broadly ovate to orbicular, about 9.5 cm, with a raised boss on its upper surface. Pitchers and peristome are deep reddish brown to almost black and glossy; inside the pitcher is bright green with purple patches. The male inflorescence can exceed two metres, the longest known in the genus.
Similar species
The closest relative is Nepenthes truncata, which also grows on Mindanao and was once named as this species' parent. It has a narrower, rounded peristome of about two centimetres with closely packed ribs, and in mature pitchers the wings are reduced to ridges without fringe. From the Bornean Nepenthes veitchii, which the broad peristome recalls, it differs in its orbicular rather than oblong lid, the pronounced appendage at the base of the lid and above all its almost glabrous, glossy surface; Nepenthes veitchii is densely hairy. Most confusing is Nepenthes nebularum from south-eastern Mindanao: also dark and with a broad peristome. The differences lie in the lid and the indumentum, and the relationship between the two is still debated.
The trap and how it works
A pitfall trap of exceptional size. The extremely broad, sloping peristome acts as a slick landing strip: the ribs stand up to one and a half millimetres high and become treacherously slippery under a film of water, so an insect alighting on the rim slides inside. Under the lid the nectar glands are densely packed around the basal appendage, right above the mouth, so visitors are drawn to a point directly over the trap. The fringed wings down the front give crawling animals a route up. At the bottom stands digestive fluid. Nothing has been published on prey in the wild; the only wild plants examined closely were gone soon after discovery.
Habitat and ecology
The original plants grew in submontane evergreen forest at about 1800 m (B1), on the ground and in full sun; a plant about one and a half metres across was not yet mature. Later sightings of similar plants elsewhere on Mindanao, by Andy Smith in 2011 and 2013 and by Wally Suarez in 2012, concerned plants growing exclusively as epiphytes, high in trees. It is thus quite possible that in nature the species lives mainly in the canopy and that the ground plants of 1997 were an exception.
Distribution and elevation
Endemic to Mindanao. The precise locality has never been published for conservation reasons, and this guide does not give it either. Whether the later sightings of epiphytic plants elsewhere truly concern the same species has not been settled, though Smith described them as morphologically similar and possibly conspecific. The elevation field gives the one published value from the type locality.
- Recorded (one-degree cells)
Forms and variation
No variation has been described from the wild population, and virtually every plant anyone has seen descends from the eleven seedlings of 1997. One of the seedlings raised in the United States produced pitchers roughly intermediate between this species and Nepenthes truncata, suggesting the two cross in the wild. It has also been proposed that Nepenthes robcantleyi is itself a natural hybrid, of Nepenthes truncata and Nepenthes nebularum; artificial crosses of those two do not look like it, however, and most authors keep both for now as closely related, separate species.
Where and when to see it
Seeing a wild plant is all but impossible: the type locality has been destroyed, other sites are not disclosed and the plants grow high in trees. The species can, however, be seen in botanic gardens and at major horticultural shows. When looking at a plant, note the ratio between the front and back of the peristome: that funnel-like flare towards the back, with ribs like little fins, is the character that separates it from Nepenthes truncata.
Conservation status
The Red List assesses the species as Endangered. Cheek rated it more severely when describing it, as Critically Endangered, noting it might already be extinct in the wild; the later sightings of epiphytic plants make that less likely. The threat is the loss of submontane forest on Mindanao to logging and agriculture, together with collecting pressure: this is one of the most coveted pitcher plants. It is listed in CITES Appendix II. That most trade runs on descendants of the 1997 seedlings eases the pressure on wild plants.
Scientific name
Nepenthes robcantleyi | Cheek, 2011
Nepenthes robcantleyi was described in 2011 by Martin Cheek of the Royal Botanic Gardens, Kew, in Nordic Journal of Botany 29(6): 677-681; an independently paginated preprint of the type description was distributed on 2 December 2011, but the journal number in which it appeared was only issued on 6 January 2012 (though dated "2011"). The original population was discovered in January 1997 on a remote mountain on Mindanao, Philippines, at approximately 1,800 m elevation in submontane evergreen forest; the exact location has never been publicly disclosed, for conservation reasons. A remote mountain on Mindanao, Philippines, at approximately 1,800 m elevation; the precise location has deliberately not been disclosed. The name honours Robert Cantley, who discovered and cultivated the species. The specific epithet "robcantleyi" was deliberately chosen to avoid confusion with an earlier, never formally published name (N. × cantleyi) already applied to a natural hybrid involving different species.
World Checklist of Vascular Plants (WCVP), via Plants of the World Online (POWO), Royal Botanic Gardens, Kew.