The flower buds are borne in groups of thirteen to twenty and are fused together in leaf axils on a flattened peduncle 12 to 35 mm (0.5 to 1.4 in) long.

[1][3][4] Eucalyptus arborella was first formally described in 2002 by Ian Brooker and Stephen Hopper from a specimen collected near the Twertup field studies centre in the Fitzgerald River National Park.

Together these eight species form series Lehmannianae, a group that have fruit with exserted valves that have fused tips even after the seeds are lost, a feature also shared with the distantly related Eucalyptus cornuta.

[3] The Twertup mallet grows in rocky places in the Fitzgerald River National Park and near Corackerup in the Esperance Plains biogeographic region.

[1][3] This eucalypt is classified as "Priority Three" by the Western Australian Government Department of Parks and Wildlife[1] meaning that it is poorly known and known from only a few locations but is not under imminent threat.