Nepenthes rigidifolia is a spectacular Indonesian pitcher plant known only from one small population near Sidikalang in the Karo Regency, North Sumatra. Originally, only 24 plants were observed in the wild (Akhriadi et al., 2004), and this appears to have been the full extent of the total known wild population of this species. Only one Nepenthes species, (N. pitopangii) is known from a smaller wild population. Unfortunately, it appears that the number of N. rigidifolia plants remaining in the wild has since declined sharply, putting this species at serious risk of extinction. Nepenthes rigidifolia grows terrestrially at altitudes of 1000–1600 m, in montane forest and scrub. It forms a branched stem up to 10 m long and naturally hybridises with N. spectabilis. Hybrids with N. spectabilis may now outnumber pure N. rigidifolia plants in the wild (Stewart McPherson, pers. observ., 2007).
The lamina is thick, stiff, leathery, spathulate, oblong or ovate, up to 21 cm long and 8 cm wide. The apex of the leaf is acute, obtuse or rounded and occasionally sub–peltate, the tendril emerging from the leaf a few millimetres below the apex. The base of the leaf is attenuate and clasps the stem. The lamina is green and the stem, midrib and tendril may be yellow, green, orange or red. The tendril, pitchers, stem and parts of the inflorescence may be lined with short orange or brown hairs up to 1 mm long, but these and all other parts of the plant may be entirely glabrous.
The lower pitchers are up to 15 cm tall and 6.5 cm wide. The traps are wholly ovate, narrowing obviously below the peristome (Figure 513). Wings up to 2 mm wide, fringed with narrow filaments up to 5 mm long, extend down the front of the pitcher for a short distance before becoming reduced to narrow ridges. The peristome is cylindrical, up to 21 mm wide, and lined with fine ribs up to 0.5 mm high, spaced up to 1 mm apart. The outer margin of the peristome is recurved and may be slightly crenellated. The inner margin curls downwards and extends into the pitcher opening for several millimetres. The ribs form teeth up to 1 mm long on the inner edge of the peristome. The lid is elliptic or ovate, often with a cordate base, up to 5.2 cm long by 3.5 cm wide, and lacks an appendage. The spur is up to 12 mm long, and may be unbranched (Stewart McPherson, pers. observ.) or trifid (Akhriadi et al., 2004).
The exterior of the lower pitchers is olive green, orange or brown, and mottled heavily with dark purple, brown or black blotches. The interior is light yellow, light green or creamy white, and speckled with dark red, dark purple or black. The peristome is dark red, dark brown or black, and the lid is dark red, dark brown or black, but often lighter on the underside.
The upper pitchers are up to 21 cm tall and 9.4 cm wide. The lower third of the pitcher is broadly infundibular, becoming ovate above. The width of the trap narrows below the peristome, as in the lower pitchers (Figure 514). The wings are entirely reduced to narrow ridges or are hardly discernible. The peristome is cylindrical, up to 25 mm wide, and lined with ribs up to 0.5 mm high, spaced up to 1 mm apart. All other parts are similar to the lower pitchers, except for the lid, which is up to 8 cm long and 4.5 cm wide.
The upper pitchers are coloured in a similar fashion to the lower pitchers, but are often lighter.
The inflorescence is a raceme, to 8 cm long. The peduncle is up to 4.2 cm long and the rachis to 3.9 cm long. Flowers are borne on 2-flowered partial peduncles, with a filiform bract to 2 mm near the base, and pedicels to 6 mm long. Tepals are ovate-oblong, to 5 mm long, and the anther head is borne on a column up to 4 mm long. Nepenthes rigidifolia is one of only a few Nepenthes species known to produce multiple inflorescences concurrently on a single stem. This has also been observed in N. ampullaria, N. benstonei, N. sanguinea (Clarke, 2001), N. alba, N. attenboroughii and especially N. philippinensis.
The lower pitchers of N. rigidifolia may appear similar to those of N. spectabilis, but these species differ strikingly in colouration, and the upper pitchers of N. rigidifolia are also broad and voluminous, rather than narrow and cylindrical, as in N. spectabilis.
Nepenthes rigidifolia may also be similar to N. bongso, N. ovata and associated species, but is distinguished from these species by its thick, stiff, leathery foliage, its narrower, generally cylindric peristome with small teeth, and its ovate upper pitchers.
A detailed description of N. rigidifolia extracted from Stewart McPherson’s Pitcher Plants of the Old World (2009) can be freely downloaded here.
Further field observations are urgently required to assess whether or not the wild population of N. rigidifolia truly is restricted to the type locality or whether the species is more widely distributed than currently believed. If the type population does represent the only occurrence of N. rigidifolia in the wild, this species is threatened with imminent extinction, or may already be extinct.
Very few genetic lineages of N. rigidifolia are in cultivation, and it is not even known if strains of both sexes are grown by horticulturists. More so than any other Nepenthes, it is critically importance that all lineages of N. rigidifolia are retained in cultivation to prevent the imminent extinction of this plant.
If you grow distinct strains of N. rigidifolia that are not in the Rare Nepenthes Collection, and are willing to donate or sell plants, cuttings or seeds of legally cultivated plants to Ark of Life, please contact the Rare Nepenthes Collection team through this contact page of this website.
If you cultivate N. rigidifolia, but are unable to contribute material to the Rare Nepenthes Collection, however would still like to help save this species, please register your plants with Ark of Life, so that we can develop a breeding programme and record all plants of this critically endangered plant in cultivation.
Nepenthes rigidifolia is not commercially available at the current time. The scarcity of plants, both in the wild and in cultivation emphasizes the real risk of total extinction of this plant.
Photos of N. rigidifolia plants in the wild.
Cultivated N. rigidifolia plants
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