It has smooth, grey bark, lance-shaped to elliptic adult leaves, spindle-shaped flower buds in groups of nine to thirteen, white flowers and barrel-shaped to cylindrical fruit.Eucalyptus capillosa is a tree or mallee that typically grows to a height of 12 metres (39 ft) and forms a lignotuber.

[5] Eucalyptus capillosa was first formally described by the botanists Ian Brooker and Stephen Hopper in 1991 from a specimen near Merredin and the description was published in the journal Nuytsia.

[5] Brooker and Hopper described two subspecies that have been accepted by the Australian Plant Census: The name polyclada is derived from the Ancient Greek words polys meaning "many"[8]: 623  and klados meaning "branch", "twig" or "stem",[8]: 162  referring to the mallee habit of this subspecies.

Other species found in the upper storey include E. salmonophloia and occasionally E. salubris, E. loxophleba subsp.

[13] This eucalypt is classified as "not threatened" by the Western Australian Government Department of Parks and Wildlife.