Nepenthes klossii, like virtually all species in the genus, is a scrambling vine.
The stem may climb to a height of several metres.

The leaves of the climbing stem are coriaceous and petiolate.
The lamina or leaf blade is oblong-lanceolate in shape and up to 25 cm long by 9 cm wide.
It has an obtuse apex and is abruptly contracted towards the petiole, which is up to 6 cm long and bears a pair of wings (≤5 mm wide).
Around three longitudinal veins are present on either side of the midrib.
They originate from the wings of the petiole and run roughly parallel to the midrib in the outer third to fourth of the lamina.
Pinnate veins are indistinct and reticulate.

Tendrils are usually 1 to 1.5 times as long as the lamina and range in diameter from 2 mm near the lamina to 5 mm near the base of the pitcher.
They often have a curl in the middle.

Rosette and lower pitchers have two wings (≤9 mm wide) running down the ventral surface of the pitcher cup.
Fringe elements are up to 7 mm long.

Upper pitchers abruptly arise from the ends of the tendrils, forming a 45 mm wide curve.
They are narrowly infundibular in shape, sometimes becoming tubulose towards the mouth.
Aerial pitchers are up to 26 cm high by 7 cm wide.
The ventral wings are usually reduced to a pair of prominent ribs in aerial pitchers.
The pitcher mouth (≤4 cm wide) is oblique at the front and elevated at the rear, although it does not form a neck.
The peristome is flattened and ranges in width from 3 mm at the front to 14 mm near the lid.
It bears a series of ribs up to 1 mm high and spaced up to 1.5 mm apart, while its inner margin is almost entire.
The glandular region is composed of tiny overarched glands and covers the lower half of the pitcher's inner surface.
The lid or operculum is suborbicular, slightly cordate at the base, and about 5 cm long by 5 cm wide.
An obtuse, laterally-flattened appendage (≤8 mm long) is present in the basal part of the midrib on the lid's lower surface.
Both the appendage and the lower surface of the lid are wholly glandular, bearing numerous deepened and rimmed glands of varying sizes.
An unbranched, attenuate spur is inserted on the highest part of the pitcher's dome, around 20 mm from the base of the lid.

Nepenthes klossii has a racemose inflorescence.
The peduncle is around 18 cm long, while the rachis reaches 14 cm in length.
Pedicels are one- to three-flowered and up to 10 mm long.
Tepals are oblong, obtuse, and around 3 mm long by 1 mm wide.
Fruits are approximately 15 mm long, being distinctly attenuate towards the base and indistinctly attenuate towards the apex.

A dense, golden indumentum is present on the underside of the lamina, composed of short spreading stellate hairs, longer branched hairs, and even longer unbranched hairs (≤7 mm long).
The upper surface of the lamina is glabrous.
The pitchers and tendrils have a similar covering of hairs to the underside of the lamina, although it is less dense.
The spur has a very dense indumentum of short hairs.
Spreading hairs cover the fruits and the outer surface of the tepals.

Pitchers are red speckled with a purple lid.
Herbarium specimens are yellowish in colour, with the inner surface of the pitcher being bluish and pruinose above the glandular region.
Nepenthes klossii, like virtually all species in the genus, is a scrambling vine. The stem may climb to a height of several metres.
The leaves of the climbing stem are coriaceous and petiolate. The lamina or leaf blade is oblong-lanceolate in shape and up to 25 cm long by 9 cm wide. It has an obtuse apex and is abruptly contracted towards the petiole, which is up to 6 cm long and bears a pair of wings (≤5 mm wide). Around three longitudinal veins are present on either side of the midrib. They originate from the wings of the petiole and run roughly parallel to the midrib in the outer third to fourth of the lamina. Pinnate veins are indistinct and reticulate. 
Tendrils are usually 1 to 1.5 times as long as the lamina and range in diameter from 2 mm near the lamina to 5 mm near the base of the pitcher. They often have a curl in the middle.
Rosette and lower pitchers have two wings (≤9 mm wide) running down the ventral surface of the pitcher cup. Fringe elements are up to 7 mm long.
Upper pitchers abruptly arise from the ends of the tendrils, forming a 45 mm wide curve. They are narrowly infundibular in shape, sometimes becoming tubulose towards the mouth. Aerial pitchers are up to 26 cm high by 7 cm wide. The ventral wings are usually reduced to a pair of prominent ribs in aerial pitchers. The pitcher mouth (≤4 cm wide) is oblique at the front and elevated at the rear, although it does not form a neck. The peristome is flattened and ranges in width from 3 mm at the front to 14 mm near the lid. It bears a series of ribs up to 1 mm high and spaced up to 1.5 mm apart, while its inner margin is almost entire. The glandular region is composed of tiny overarched glands and covers the lower half of the pitcher's inner surface. The lid or operculum is suborbicular, slightly cordate at the base, and about 5 cm long by 5 cm wide. An obtuse, laterally-flattened appendage (≤8 mm long) is present in the basal part of the midrib on the lid's lower surface. Both the appendage and the lower surface of the lid are wholly glandular, bearing numerous deepened and rimmed glands of varying sizes. An unbranched, attenuate spur is inserted on the highest part of the pitcher's dome, around 20 mm from the base of the lid.
Nepenthes klossii has a racemose inflorescence. The peduncle is around 18 cm long, while the rachis reaches 14 cm in length. Pedicels are one- to three-flowered and up to 10 mm long. Tepals are oblong, obtuse, and around 3 mm long by 1 mm wide. Fruits are approximately 15 mm long, being distinctly attenuate towards the base and indistinctly attenuate towards the apex.
A dense, golden indumentum is present on the underside of the lamina, composed of short spreading stellate hairs, longer branched hairs, and even longer unbranched hairs (≤7 mm long). The upper surface of the lamina is glabrous. The pitchers and tendrils have a similar covering of hairs to the underside of the lamina, although it is less dense. The spur has a very dense indumentum of short hairs. Spreading hairs cover the fruits and the outer surface of the tepals.
Pitchers are red speckled with a purple lid. Herbarium specimens are yellowish in colour, with the inner surface of the pitcher being bluish and pruinose above the glandular region.
Nepenthes klossii