Nepenthes Dubia - Description

Description

Nepenthes dubia is a climbing plant. The stem can reach 3 m in length and is 3 to 4 mm in diameter. It is cylindrical or slightly angular. Internodes are up to 10 cm long.

A rosette plant, showing the reddish stem of this species (left) and a closeup of a rosette pitcher (right)

Leaves are sessile and coriaceous. The lamina is lanceolate-spathulate in form. It may be up to 10 cm long and 2 cm wide. It has an acute apex and is gradually attenuate towards the base, which clasps the stem for one third to a half of its circumference. Around three pairs of longitudinal veins are present on the lamina, originating from the basal third of the midrib. Pinnate veins are oblique and irregularly reticulate, although they are not easily distinguishable. Tendrils can be up to 15 cm long and may or may not have a curl.

Rosette and lower pitchers are rarely produced. They are narrowly infundibular in the lower two-thirds, becoming ovoid above, and are sharply contracted below the rim. Terrestrial pitchers are relatively small, reaching 5 cm in height and 3.5 cm in width. A pair of fringed wings (≤3 mm wide) runs down the upper third of the pitcher beneath the rim. The glandular region covers the lower two-thirds of the inner surface. The pitcher mouth is round and slightly raised at the back. The peristome is cylindrical, up to 3 mm wide, and bears indistinct teeth. The lid or operculum is ovate and slightly raised in the middle. It bears no appendages. An unbranched spur (≤4 mm long) is inserted at the base of the lid.

Upper pitchers are generally larger, growing to 8 cm in height and 4 cm in width. They gradually arise from the ends of the tendrils, forming a 5 to 10 mm wide curve. They are tubular to infundibular in the lower parts with laterally appressed pitcher walls. As in N. inermis, 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 inner surface of the pitcher is covered with numerous small, slightly depressed glands, occurring at a density of 600-900 per square centimetre; it lacks a waxy zone. The pitcher mouth is ovate, horizontal, and acute towards the lid. It bears a cylindrical or involute peristome (≤4 mm wide) with indistinct teeth spaced 0.25 to 0.5 mm apart. The inner portion of the peristome accounts for around 45% of its total cross-sectional surface length. The lid is narrowly cuneate, without appendages, and up to 4 cm long and 0.7 cm wide. It is rounded at the apex, gradually attenuate towards the base, and bears numerous small round or elliptical glands on its undersurface. Characteristically, it is almost always reflexed beyond 180 degrees relative to the pitcher mouth. In upper pitchers, the unbranched spur is 3 to 5 mm long.

Nepenthes dubia has a racemose inflorescence that is distinctly short and compact. The peduncle may be up to 8 cm long. The rachis grows to 10 cm in length, although it is usually shorter in female inflorescences. Pedicels are bracteolate and up to 8 mm long. Sepals are oblong-lanceolate and up to 3 mm long.

Most parts of the plant are virtually glabrous. Inflorescences sometimes bear a sparse indumentum of simple hairs. Caducous brown hairs are present on developing pitchers.

The stem, inflorescence and tendrils are characteristically purplish-red in most plants. The lamina is green, often with a red midrib. Pitchers generally range in colour from light green to yellow throughout, although orange and red forms are also known to exist. Danser described the colour of herbarium specimens as "fallow-dun, here and there blackish".