P. robustus is an exemplar of a globose-shaped cactus with a solitary posture. It has a dark green stem, equipped with well marked tubercles on which can be noticed the white and woolly areoles. Radial and central spines emerge from the latter: the radials are long and brown with dark tips, while the central ones are more robust, longer and also have darker tips. Both are curved upwards. In the more mature exemplars, the spines tend to assume greyish hues. During the flowering period, P. robustus gives beautiful flowers in the shape of a daisy, with delicate petals and bright colors such as orange; red, yellow and white and enriched by a median line of darker shades. Synonym: Eriosyce curvispina var. robusta