Pseudoeurycea mystax is a species of salamander in the family Plethodontidae. It is endemic to Mexico and only known from the area of its type locality in the Sierra Madre de Oaxaca near Ayutla, Oaxaca. Its common name is mustache false brook salamander or mustached false brook salamander. The specific name refers to the whitish protuberances on the lips that resemble a mustache in the frontal view of the male holotype.

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