Moranopteris inaccessa, here described and illustrated, is a new species from southern Peru. Plants were collected in the Abra Málaga private conservation area from steep ledges accessible only with mountaineering equipment. Moranopteris inaccessa differs from its congeners by the combination of elongate membranaceous laminae that are 1-pinnate-pinnatifid. Found at 4,427 m, its distribution is over 500 m higher in elevation than any other species of Moranopteris. Phylogenetic analyses of atpß, rbcL, and trnL-trnF molecular sequences, using maximum parsimony, maximum likelihood, and Bayesian analysis support M. inaccessa as sister to M. longisetosa. The two are similar in their elongate and highly divided leaves compared to other species of Moranopteris. The discovery of this new species highlights the value of undertaking botanical surveys of undisturbed vegetation patches in the high Andes that potentially host unrecognized plant diversity.