P. comma is very similar in appearance to P. tetronycha but can be distinguished as it is a larger moth with slightly different colouration on, as well as shape of, its forewings.

P. comma may possibly be declining in population and as at 2017 a reassessment of its conservation status is regarded as being needed.

This species was originally described by Francis Walker in 1856 and named Mamestra comma.

[3][2] The female holotype specimen was collected by Reverend John Frederick Churton.

[2] J. S. Dugdale presumed Churton collected this specimen in Auckland however Robert Hoare has hypothesised that Wellington may possibly be the type locality for this species.

[5] In 1868 Achille Guenée replaced Walker's comma name with Nitocris bicomma.

[6] In 1887 Edward Meyrick synonymised both this name and Graphiphora implexa and moved the species into the Orthosia genus.

[2] As a result of the previous confusion with P. tetronycha, as at 2017 there is currently no description of P. comma larva that does not also relate to P.