Nepenthes Rigidifolia - Description

Description

Nepenthes rigidifolia is a climbing plant. The stem, which may be branched, is cylindrical and up to 1.3 cm in diameter. It can attain a length in excess of 10 m. Internodes are up to 5.1 cm long.

Leaves are sessile to broadly sub-petiolate and have a coriaceous texture. They are noted for being particularly thick and rigid. The lamina is usually spathulate-oblong, but may also be ovate in rosettes. It reaches a maximum recorded length of 20.8 cm and width of 7.8 cm. It is gradually attenuate towards the base, clasping the stem for half to two-thirds of its circumference. The apex of the lamina is usually obtuse-rounded in rosettes and obtuse-acute on leaves of the climbing stem, but may also be acuminate-acute. It may be sub-peltate in some specimens, with the tendril attachment being located subapically, up to 9 mm from the laminar apex. The midrib may be flattened or sunken on the upper surface and bulges outwards on the lower. Two to four longitudinal veins are present on either side of the midrib. Pinnate veins are distinct on the upper surface of the lamina and indistinct on its underside. Tendrils are up to 32.1 cm long and may or may not have a loop.

Rosette and lower pitchers are broadly ovoid throughout, narrowing somewhat towards the orifice. They grow up to 15 cm in height by 6.4 cm in width. A pair of fringed wings (≤2 mm wide) extends up to 2 cm below the peristome, before narrowing to ribs. These wings may bear fringe elements up to 5 mm long. The pitcher mouth is elliptic-ovate and has an oblique insertion, measuring up to 6.7 cm by 4.7 cm. The peristome is cylindrical, expanded, and up to 2.1 cm wide. It may be slightly raised at the front, forming a notch up to 1.1 cm long. It bears ribs up to 0.5 mm high and spaced up to 1 mm apart. The inner margin of the peristome is lined with very small but distinct teeth measuring 0.5–1 mm in length. The outer margin is recurved and may be sinuate to some degree. The peristome is elongated into a neck up to 6.7 cm long and 4.7 cm wide. The glandular zone covers the lower half of the inner surface. The pitcher lid is sub-orbicular to elliptic-ovate and may be up to 5.2 cm long by 3.5 cm wide. It often has a cordate base and acute-obtuse apex. Three longitudinal veins are present on either side of the lid. A number of circular or slightly ovate nectar glands (≤ 0.1 mm wide) are concentrated on the underside of the lid, but no appendages are present. A spur measuring up to 12 mm in length is inserted around 2 mm below the apex of the neck. It may be simple (unbranched) or trifid.

Upper pitchers are similar in most respects to their lower counterparts. They are broadly infundibular in the lower third and ovoid above, narrowing below the pitcher opening. They are also larger, reaching 21.1 cm in height and 9.4 cm in width. Wings are reduced to narrow ribs that run the whole length of the pitcher cup. The peristome is cylindrical and up to 4.4 cm wide. As in lower pitchers, it bears ribs up to 0.5 mm high and spaced up to 1 mm apart. The lid is up to 7.9 cm long and 5.6 cm wide. The spur, reported to be bifid (with each branch being two-branched itself) and up to 16 mm long, is inserted near the base of the lid.

Nepenthes rigidifolia has a racemose inflorescence. Female inflorescences have not been recorded in the wild. In male inflorescences, the rachis measures around 3.9 cm in length and the peduncle around 4.2 cm. Bracts are approximately 9 mm long by 4 mm wide. Flowers are produced on two-flowered partial peduncles bearing filiform basal bracteoles up to 2 mm long. The unbranched portion of the partial peduncles is up to 5 mm long. The pedicels themselves are up to 6 mm long. Tepals are ovate-oblong and measure up to 5 mm in length by 3 mm in width. The androphore is around 4 mm long and 1 mm in diameter. Nepenthes rigidifolia is one of the few Nepenthes species known to occasionally produce multiple inflorescences concurrently on a single stem. This unusual reproductive habit has also been observed in N. alba, N. ampullaria, N. attenboroughii, N. benstonei, N. philippinensis, N. sanguinea, and N. thai.

The development of the indumentum is variable in this species. Some plants are completely glabrous, while others bear a covering of orange to brown hairs (≤1 mm long) on the stem, pitchers, tendrils, and portions of the inflorescence. Developing rosette pitchers and tendrils are often densely pubescent, while developing pitchers produced on the climbing stem are tomentose. The pitcher lid may be glabrous or pubescent. The peduncle is typically slightly pubescent, and the partial peduncles, pedicels, bracts, tepals, and androphores densely pubescent.

The laminae are green, whereas the stem, midribs and tendrils range from green, through yellow, to orange or even red. Terrestrial pitchers have a distinctive colouration: their outer surface is black, brown, or purple, with numerous large flecks of greenish-white, brown, or orange. The upper part of the inner surface ranges from white to light green or light yellow, with dark red to black blotches. Both the peristome and lid may be dark red, dark brown, or even black, although the latter is commonly lighter on its lower surface. The pigmentation of the upper pitchers is generally similar to that of the lowers, although typically lighter. The describing authors observed that rosette pitchers typically have a dark brown peristome, whereas that of upper pitchers is often orange to dark red. Herbarium specimens have an almost black stem. Dried leaves are light brown above with a dark brown underside, whereas pitchers are blackish-brown with dark brown blotches and an almost black lid.

No infraspecific taxa of N. rigidifolia have been described.