It is one of the smallest species of Platyomus in Argentina (6mm long), along with P. elengatulus.
P. dianae differentiates by the cream to brown vestiture, with lighter stripes along the disc of pronotum and two "v-shaped" lighter stripes on the elytra. There is also a cream morphotype with stripes almost indistinct. Eyes are less convex than in other Argentinean species and elytra are more slender and lacking tubercles.
Unknown.
It is associated with vegetation of the Paranaense forest.