The fruit is a woody, conical capsule 5–10 mm (0.20–0.39 in) long and wide with the valves close to rim level.

[2][3][4] Some other ironbarks occurring in the same area including E. siderophloia, E. rhombica and E. decorticans are similar but all have smaller buds and fruit, and a much shorter operculum than that of E.

[2] Eucalyptus fibrosa was first formally described in 1859 by Victorian state botanist Ferdinand von Mueller in 1859 from a collection from the Brisbane River and the description was published in Journal and Proceedings of the Linnean Society, Botany.

[2] In 1962, Lawrie Johnson and Robert Anderson described two subspecies and the names have been accepted by the Australian Plant Census: Red ironbark grows in forest on shallow, relatively infertile soil.

It is widespread on the coast, tablelands and nearby inland areas from near Rockhampton in Queensland to Moruya in New South Wales.