Polysteganus undulosus was first formally described as Dentex undulosus in 1908 by the English zoologist Charles Tate Regan with its type localities given as 16 miles northeast of Bird Island, KwaZulu-Natal, and Table Bay, Cape Colony, in South Africa.

[3] The genus Polysteganus is placed in the family Sparidae within the order Spariformes by the 5th edition of Fishes of the World.

Its specific name undulosus, which means ""with undulating lines", a reference to the wavy light-edged dark horizontal stripes on the upper body.

The dorsal profile of the head is moderately steep up to the nape, with a prominent bump above the eyes in juveniles but this is lacking in adults.

A large oval dark blotch is on the flanks underneath the spiny part of the dorsal fin.

The juveniles are largely resident but the adults migrate norteards frpm the southern coasy of South Africa north to the eastern coast in the winter months to spawn.

[1] This species is a rudimentary hermaphrodite, i.e. the gonads contain both male and female tissue, and functional gonochorist, they do not change sex.

During spawning the adults aggregate over offshore reefs between 50 and 100 m (160 and 330 ft) in depth off the eastern coast of South Africa in KwaZulu-Natal and the Transkei Each female bears between 1,000,000 and 3,000,000 eggs.