"Nepenthes benstonei" appears to be related to "N. sanguinea", which is also native to Peninsular Malaysia. It can be distinguished on the basis of its significantly larger leaves, which are often sub-petiolate and differ in shape. "Nepenthes benstonei" also has longer tendrils and a denser indumentum. The presence of teeth on the peristome of lower pitchers and of a thick, waxy cuticle on the leaves also serve to distinguish these taxa. In addition, herbarium specimens of "N. benstonei" tend to dry to a lighter colour than those of "N. sanguinea".