The larvae of stoneflies (Plecoptera) are important indicators for monitoring aquatic ecosystems, but the immature stages of some relevant species have not been described. Here, mitochondrial gene sequences are used to associate the adult and larval life stages for species of Newmanoperla McLellan. This study finds molecular and morphological support for five species, which include the four previously described species (N. exigua, N. hackeri, N. prona and N. thoreyi) and a newly recognised species, N. theischingeri, sp. nov., which is described herein. Molecular divergences between species for the COI fragment had minimum values of 15–18% while the maximum intraspecific divergence was 6–9%, and there was no overlap between species. Morphological characters for distinguishing the larvae of the five species were observed on the femora and included variations in the type of setation present and the area of occurrence. The combination of molecular and morphological methods enabled the larval morphology to be reassessed and has led to the following outcomes: the first formal generic larval description, a newly recognised species, updated descriptions for larvae of all species of Newmanoperla and a dichotomous key to larvae.