It is a relatively large moth that is superficially unlike any other species in North America.

It is most closely related to Hypotrix quindiensis (Draudt, 1924) that was originally described as a form of H. lunata; it occurs from Colombia to Peru.

Hypotrix purpurigera and several of its South American relatives also have black reniform and orbicular spots that are frequently fused posteriorly, creating a wide V-shaped mark.

Within the North American fauna the male genitalia of Hypotrix lunata are most similar to those of Hypotrix hueco, but differ in that only the apical part of the uncus is expanded in H. lunata whereas the apical 2/3 is wide in H. hueco, the clasper is stouter and abruptly tapered apically in H. lunata, and the dorsal lobe on the sacculus is much larger.

The vesica is very different from that of H. hueco in having much more extensive basal cluster of spines and subbasal cornuti in a longitudinally ribbed basal swelling, and the vesica has three tight medial coils rather than one as in H. hueco.