Nepenthes inermis is a tropical pitcher plant endemic to the Indonesian island of Sumatra. The specific epithet inermis is Latin for "unarmed" and refers to the upper pitchers of this species, which are unique in that they completely lack a peristome.
Botanical history Nepenthes inermis was first collected on September 7, 1918, by H. A. B. Bünnemeijer on Mount Talang, at an altitude of 2,590 metres (8,500 ft) above sea level.[note a] Two further collections were made by Bünnemeijer on Bukit Gombak on November 16, 1918, at 2,300 metres (7,500 ft)[note b] and 2,330 metres (7,640 ft)[note c] A fourth specimen was taken on April 26, 1920, from an elevation of 1,800 metres (5,900 ft) on Mount Kerintji.[note d] This final specimen, Bünnemeijer 9695, was later designated as the lectotype of N. inermis by Matthew Jebb and Martin Cheek.
Nepenthes inermis was first illustrated in an issue of De Tropische Natuur published in 1927. A year later, B. H. Danser formally described N. inermis in his seminal monograph "The Nepenthaceae of the Netherlands Indies".[note e] He wrote: "This new species is easily distinguishable from all others by the peculiar pitchers without peristome and with very narrow lid. Probably it is most nearly related to N. Bongso." Several of the specimens collected by Bünnemeijer were labeled with the local vernacular names galoe-galoe antoe and kandjong baroek. Danser noted that these originate from the Minangkabau language and are also used to refer to other species, but stated that their meaning was not clear to him. In 1986, Mitsuru Hotta and Rusjdi Tamin included plant material belonging to N. dubia and N. inermis in their description of N. bongso. In a 1993 study of Nepenthes prey and pitcher infauna, the same authors, together with M. Kato and T. Itino, identified N. inermis from Mount Gadut as N. bongso. Despite this taxonomic confusion, N. bongso differs considerably in pitcher morphology from N. inermis and is not easily confused with it.
Description Nepenthes inermis is a climbing plant. The stem, which may be branched, reaches 7 metres (23 ft) in length and is up to 0.5 centimetres (0.2 in) in diameter. It is cylindrical-triangular in cross section. Internodes are up to 10 centimetres (4 in) long.
Leaves are sessile and coriaceous. The lamina is lanceolate-spathulate in form. It may be up to 12 centimetres (5 in) long and 3 centimetres (1.2 in) wide. It has an acute or obtuse apex and is gradually attenuate towards the base, which clasps the stem and is not decurrent. Three longitudinal veins are present on either side of the midrib. Pinnate veins are reticulate. Tendrils can be up to 15 centimetres (6 in) long and may or may not have a curl. Rosette and lower pitchers are rarely produced. They are infundibular in the lower two-thirds to three-quarters, and ovoid above. They are distinctly constricted just below the peristome. Terrestrial pitchers grow to 8 centimetres (3 in) in height and 3 centimetres (1.2 in) in width. Fringed wings are usually absent, but may be present in the upper part. The pitcher mouth is round and horizontal, and raised slightly towards the rear. The peristome is cylindrical, up to 0.3 centimetres (0.12 in) wide, and bears indistinct teeth. The lid or operculum is ovate and lacks appendages. An unbranched spur (less than 0.4 centimetres (0.16 in) long) is inserted at the base of the lid.
The unusual upper pitchers of N. inermis are larger than its lower pitchers, growing to 9 centimetres (3.5 in) in height and 5 centimetres (2 in) in width. They gradually or abruptly arise from the ends of the tendrils, forming a 1–2 centimetres (0.4–0.8 in) wide curve. They are tubular to infundibular in the lower two-thirds with laterally appressed pitcher walls. As in N. dubia, there is almost no gap between the walls in mature pitchers. The upper part of the pitcher is widely infundibular throughout. Wings are reduced to ribs in upper pitchers. The mouth is round and either horizontal or slightly raised at the front and rear. The inner surface of the pitcher is often said to be glandular throughout with no waxy zone, but one source states that the waxy zone is merely reduced. Mature upper pitchers are generally considered to completely lack a peristome, a trait that is unique to this species, although one source gives a peristome width of 0.7 millimetres (0.03 in) for an 8 centimetres (3 in) tall upper pitcher (the inner portion of the peristome is said to account for 20% of its total cross-sectional surface length, the lowest proportion among studied species). The lid is very long, narrow, and cuneiform. It is never reflexed beyond 90 degrees relative to the mouth. Nepenthes inermis has a racemose inflorescence. The peduncle may be up to 5 centimetres (2 in) long. The rachis grows to 15 centimetres (6 in) in length, although it is usually shorter in female inflorescences. Pedicels are bracteolate and up to 0.8 centimetres (0.3 in) long. Sepals are oblong-lanceolate and up to 0.3 centimetres (0.12 in) long. Young parts of the plant, such as developing pitchers, are covered in a dense indumentum. However, most hairs are caducous and mature parts are virtually glabrous. An exception to this are the hairs on the ovary and some other parts of the inflorescence, which may be persistent. The stem, inflorescence and tendrils are characteristically purplish-red in most plants. The lamina is green, often with a red midrib. Pitchers are yellowish-green. Danser described the colour of herbarium specimens as "blackish in all parts".
Ecology
Nepenthes inermis is endemic to a number peaks in the Barisan Mountains that line the western side of Sumatra. More specifically, it is known only from the Indonesian provinces of West Sumatra and Jambi. The species has an altitudinal distribution of 1,500–2,600 metres (4,900–8,500 ft) above sea level. It usually grows as an epiphyte in mossy forest, but also occurs terrestrially in stunted upper montane vegetation above 2,000 metres (6,600 ft). Substantial populations of this species are present on Mount Talang, Mount Gadut, and Mount Belirang. Nepenthes inermis is particularly abundant on the western slopes of the latter, where it grows terrestrially. It has also been recorded from Mount Gadang in West Sumatra. The conservation status of N. inermis is listed as Least concern on the IUCN Red List.
Carnivory
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