[2] Micranthocereus purpureus typically grows unbranched with columnar shoots, reaching heights of over 3 meters and diameters up to 12 centimeters.

It has 12 to 25 low, wide ribs and large, closely spaced areoles covered in white wool.

The cephalium, up to 1 meter long and 12 centimeters wide, is composed of grayish white wool and reddish brown to black bristles up to 2 centimeters long.

The red fruits, spherical to top-shaped, grow up to 2.5 centimeters long.

The specific epithet purpureus, meaning 'purple' in Latin, refers to the flower color.