Mazaediothecium uniseptatum is a species of calicioid lichen in the family Pyrenulaceae.

Found in French Guiana, it was formally described as a new species in 2015 by Dutch lichenologist André Aptroot.

The type specimen was collected near the village sentier Limonade in Saül at an altitude of 300 m (980 ft); here, in a mixed forest, the lichen was found growing on the higher trunk of a Protium tree.

It has a dull, greyish-white thallus that lacks a cortex and is surrounded by a brown prothallus line.

Ascospores are pale grey with a shape ranging from ellipsoid to spindle-shaped (fusiform), and measure 7.0–12.0 by 5.0–7.5 μm; they contain a single septum.