Nepenthes rigidifolia — Vorstman's Guide to the Carnivorous Plants

Identification

A robust climber whose stem consists of three parts: a rosette and lower section of about 30 cm and up to 8 mm thick with very short internodes, an erect middle section of 1 to 1.5 m and 1 to 1.3 cm thick, and a climbing upper section of 1 to 2 m, sometimes with spine-like nodes. The leaves are thick and stiffly leathery. In the rosette they are ovate to spathulate, 8.5 to 10 cm long; on the middle section spathulate-oblong, 19 to 21 cm long and 7 to 7.6 cm wide, with four longitudinal veins on each side and looped tendrils of 24 to 27 cm; on the climbing section 18 to 20 cm long. Lower pitchers are broadly ovoid, 9.6 to 15 cm tall and 4.4 to 6.4 cm wide, with a peristome of 0.6 to 2.1 cm and a lid of 4 to 5.2 cm. Intermediate pitchers reach 20 cm; upper pitchers are ovoid, 20.7 to 21.1 cm tall and 7.2 to 9.4 cm wide, with a peristome of 2.2 to 4.4 cm, a lid of about 6 to 8 cm and a forked spur of 1 to 1.6 cm. The pitchers are dark with flecks outside, white to pale yellow with red-black blotches inside.

Similar species

Resembles Nepenthes bongso and N. spectabilis, but differs from both in its ovoid upper pitchers, thicker, stiffer blades and forked spur. N. spectabilis has slender, narrowly funnel-shaped upper pitchers and a very long, undivided spur; N. bongso has much more slender upper pitchers. N. ovata has thinner leaves and a tendril arising at the leaf tip, not just below it. The natural hybrid with N. spectabilis is the main identification problem in the field, since it may now outnumber the pure plant.

The trap and how it works

A large pitfall with a broad peristome, especially on the upper pitchers, where it can be up to 4.4 cm wide. Nectar glands on the peristome and under the lid lure prey; the ribbed surface turns slippery when wet. Lower pitchers catch walking animals in the litter, the large ovoid upper pitchers also flying insects. The dark outside and the pale, blotched inner wall create strong contrast around the mouth.

Habitat and ecology

Lower montane forest and scrub (B1, B5), between about 1000 and 1500 m (other records to 1600 m). The plants grow on the ground; young plants have sometimes been found on rocky outcrops. The habitat lies outside protected areas and is heavily degraded.

Distribution and elevation

Endemic to Sumatra, and known only from one small area in the Barisan range of North Sumatra province. Because the species is critically endangered, this guide gives no more precise locality. The world checklist gives Sumatra as its only area.

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 or forms have been described. One natural hybrid is known, with N. spectabilis. At the only site that cross has become so numerous that it may outnumber pure N. rigidifolia; with a population of a few plants the species also risks being absorbed genetically into its relative.

Where and when to see it

Do not seek this species out. The population may be down to a few plants, and every visit, every trampling of the site and every shared location increases the risk of the last plants disappearing. Anyone who sees a pitcher plant with stiff, thick leaves and large, ovoid, dark pitchers in the uplands of North Sumatra should report it to researchers at an Indonesian university or herbarium, without making the site public.

Conservation status

Assessed on the Red List as Critically Endangered. The only known population numbered 24 mature plants in 2003 and may since have fallen to two. The site is unprotected and threatened by deforestation, forest fires and poaching; in addition, there is the risk of merging with N. spectabilis. As a member of the genus it is listed in CITES Appendix II. Since 2010 there has been a programme for ex-situ conservation of this and several other threatened species.

Scientific name

Nepenthes rigidifolia | Akhriadi, Hernawati & Tamin, 2004

Nepenthes rigidifolia was described on 22 November 2004 by Pitra Akhriadi, Hernawati and Rusjdi Tamin, in Reinwardtia 12(2): 141-144. The holotype was collected on 11 December 2003 near Sidikalang, Karo Regency, North Sumatra, at 1,000-1,500 m elevation, and is held at the Herbarium Universitas Andalas (ANDA), Padang; an isotype is held at Herbarium Bogoriense (BO), Java. Near Sidikalang, Karo Regency, North Sumatra, Indonesia, at 1,000-1,500 m elevation. The specific epithet is formed from the Latin "rigidus" ("rigid") and "folia" ("leaves"), referring to the plant's stiff, coriaceous leaf blades.

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