In external appearance P. australiana is indistinguishable from Plutella xylostella, a global pest of cruciferous plants.

Both species exhibit significant, overlapping variation in forewing pattern.

Most specimens of both species have the pale, scalloped band along the hind/dorsal margin typically used to recognize P. xylostella.

That band varies from strongly marked to nearly indistinct (the latter particularly so in females) in both species.

P. xylostella is thought to feed on a wide variety of cruciferous plants in Australia, including native and introduced species.