[3] The species was identified by Wise in 1958, based on a specimen collected from the Tongariro area of the North Island Volcanic Plateau in 1930 by Alfred Philpott.

[5] P. bistirpis is brownish-yellow in colour, with rows of minute spots freckled on its forewings.

[6] Wise's original text (the type description) reads as follows: Testaceous; ANTERIOR WINGS closely irrorated with rows of almost colourless spots between the veins.

[3]The hindwings of P. bistirpis are similar to P. hudsoni, but can be identified due to the enlarged setae and inconspicuous humeral vein.

[8] It is found in seepages in New Zealand bush,[6] and is believed to be reliant on forested ecosystems.