The stem of N. mapuluensis can measure up to 6 mm in diameter, but the maximum length is unknown.
Internodes are cylindrical and up to 4 cm long.
The leaves are coriaceous.
The lamina is oblanceolate-linear in morphology, up to 26 cm long, and 5 cm wide.
The apex of the lamina is acute, while the base is attenuate, sub-petiolate, and semi-amplexicaul.
Tendrils grow to 50 cm in length.

The pitchers of N. mapuluensis are ellipsoidal in shape.
They grow to 21 cm in height and 8.5 cm in diameter.
The pitchers possess two fringed wings up to 10 mm wide.
The peristome of this species is moderately developed and is folded or wavy as in the closely related N. northiana.
The peristome may be up to 12 mm wide and bears a row of distinct, but not pronounced, teeth.
Aerial or upper pitchers may be infundibular throughout, but are often cylindrical and relatively small.
They bear reduced fringed wings or ribs.

Nepenthes mapuluensis has a racemose inflorescence.
The peduncle is up to 7 cm long.
The size of the rachis is unknown.
Pedicels grow to 8 mm in length.
A study of 120 pollen samples taken from the type specimen (Kostermans 14017) found the mean pollen diameter to be 28.9 μm (SE = 0.5; CV = 9.2%).

The species is mostly glabrous, although certain parts of the plant, such as the pitchers, may have a scattered indumentum of short hairs.
The stem of N. mapuluensis can measure up to 6 mm in diameter, but the maximum length is unknown. Internodes are cylindrical and up to 4 cm long. The leaves are coriaceous. The lamina is oblanceolate-linear in morphology, up to 26 cm long, and 5 cm wide. The apex of the lamina is acute, while the base is attenuate, sub-petiolate, and semi-amplexicaul. Tendrils grow to 50 cm in length.
The pitchers of N. mapuluensis are ellipsoidal in shape. They grow to 21 cm in height and 8.5 cm in diameter. The pitchers possess two fringed wings up to 10 mm wide. The peristome of this species is moderately developed and is folded or wavy as in the closely related N. northiana. The peristome may be up to 12 mm wide and bears a row of distinct, but not pronounced, teeth. Aerial or upper pitchers may be infundibular throughout, but are often cylindrical and relatively small. They bear reduced fringed wings or ribs.
Nepenthes mapuluensis has a racemose inflorescence. The peduncle is up to 7 cm long. The size of the rachis is unknown. Pedicels grow to 8 mm in length. A study of 120 pollen samples taken from the type specimen (Kostermans 14017) found the mean pollen diameter to be 28.9 μm (SE = 0.5; CV = 9.2%).
The species is mostly glabrous, although certain parts of the plant, such as the pitchers, may have a scattered indumentum of short hairs.
Nepenthes mapuluensis