Tropical pitcher plant (Nepenthes inermis)

Description

Nepenthes inermis /nɪˈpɛnθiːz ɪˈnɜːrmɪs/ is a tropical pitcher plant endemic to 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. 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".