Nepenthes flava is thought to be closely related to both N. inermis and N. jacquelineae.
However, it cannot be a natural hybrid between these species as it does not occur sympatrically with them.

The pitchers of N. flava bear a close resemblance to those of N. jacquelineae.
Nepenthes flava differs from this species in that its upper pitchers are markedly smaller and have a peristome that is significantly narrower, bears distinct ribs, and has an undulate margin.
In addition, the upper pitchers of N. jacquelineae are not known to be yellow throughout, a colouration that is characteristic of N. flava.

With N. inermis, this species shares similarly infundibular pitchers, a narrow lid, and the habit of rapidly transitioning from a rosette to a climbing plant (with associated sudden internode elongation).
Furthermore, the seedling pitchers of these two species can appear quite similar.
Nepenthes inermis differs most obviously in having upper pitchers that completely lack a peristome and in lacking conspicuous glands on the underside of the lid.

The describing authors considered N. flava to likely represent an evolutionary link between the pair of N. inermis and N. jacquelineae and "common Sumatran species such as N. ovata".
They further speculated:
Nepenthes flava might represent an intermediate between N. ovata of northern Sumatra and the unusual N. inermis of the western Sumatran mountains, and would confirm Danser’s hypothesis in which he united common species familiar to him, i.e. N. bongso, N. carunculata Danser and N. singalana, with the distinctive species N. inermis and N. dubia Danser into the subgenus Montanae Danser (Danser, 1928).
Nepenthes ovata, N. jacquelineae and others were not known at this time, but it seems likely he would have included them in subgenus Montanae as well.

Other species that produce somewhat similarly shaped upper pitchers include N. eymae, N. jamban, N. pitopangii, N. talangensis, and N. tenuis.
Nepenthes flava can be distinguished from all of these species on the basis of a combination of features: entirely yellow upper pitchers; a broad, wavy peristome; very small peristome teeth; and a narrowly ovate or elliptic lid that lacks appendages (or has a small basal crest).
Furthermore, compared to many of these species, and particularly N. eymae, N. flava is a diminutive plant.
Nepenthes flava is thought to be closely related to both N. inermis and N. jacquelineae. However, it cannot be a natural hybrid between these species as it does not occur sympatrically with them.
The pitchers of N. flava bear a close resemblance to those of N. jacquelineae. Nepenthes flava differs from this species in that its upper pitchers are markedly smaller and have a peristome that is significantly narrower, bears distinct ribs, and has an undulate margin. In addition, the upper pitchers of N. jacquelineae are not known to be yellow throughout, a colouration that is characteristic of N. flava.
With N. inermis, this species shares similarly infundibular pitchers, a narrow lid, and the habit of rapidly transitioning from a rosette to a climbing plant (with associated sudden internode elongation). Furthermore, the seedling pitchers of these two species can appear quite similar. Nepenthes inermis differs most obviously in having upper pitchers that completely lack a peristome and in lacking conspicuous glands on the underside of the lid.
The describing authors considered N. flava to likely represent an evolutionary link between the pair of N. inermis and N. jacquelineae and "common Sumatran species such as N. ovata". They further speculated:
Nepenthes flava might represent an intermediate between N. ovata of northern Sumatra and the unusual N. inermis of the western Sumatran mountains, and would confirm Danser’s hypothesis in which he united common species familiar to him, i.e. N. bongso, N. carunculata Danser and N. singalana, with the distinctive species N. inermis and N. dubia Danser into the subgenus Montanae Danser (Danser, 1928). Nepenthes ovata, N. jacquelineae and others were not known at this time, but it seems likely he would have included them in subgenus Montanae as well.
Other species that produce somewhat similarly shaped upper pitchers include N. eymae, N. jamban, N. pitopangii, N. talangensis, and N. tenuis. Nepenthes flava can be distinguished from all of these species on the basis of a combination of features: entirely yellow upper pitchers; a broad, wavy peristome; very small peristome teeth; and a narrowly ovate or elliptic lid that lacks appendages (or has a small basal crest). Furthermore, compared to many of these species, and particularly N. eymae, N. flava is a diminutive plant.
Nepenthes flava