The profuse fragrant, golden flowers appear in late winter and spring, followed by long seed pods.

Explorer Thomas Mitchell collected the type specimen, from which George Bentham wrote the species description in 1842.

Plants are cross-pollinated by several species of honeyeater and thornbill, which visit nectaries on the phyllodes and brush against flowers, transferring pollen between them.

[5] Field observations at Hale Conservation Park show the bulk of new growth occurs over spring and summer from October to January.

[4] Developing after flowering has finished, the seed pods are flattish, straight or slightly curved, 5–14 cm (2–6 in) long and 5–8 mm wide.

[8][9] They are initially bright green, maturing to dark brown and have slight constrictions between the seeds,[10] which are arranged in a line in the pod.

[13] The type specimen was collected by the explorer Thomas Mitchell in present-day northern Victoria between Pyramid Hill and the Loddon River.

[1] Johann Georg Christian Lehmann described Acacia petiolaris in 1851 from a plant grown at Hamburg Botanic Gardens from seed said to be from the Swan River Colony (Perth).

Bentham classified both as A. pycnantha in his 1864 Flora Australiensis, though he did categorise a possible subspecies angustifolia based on material from Spencer Gulf with narrower phyllodes and fewer inflorescences.

[18] In 1921 Joseph Maiden described Acacia westonii from the northern and western slopes of Mount Jerrabomberra near Queanbeyan in New South Wales.

His colleague Richard Hind Cambage grew seedlings and reported they had much longer internodes than those of A. pycnantha, and that the phyllodes appeared to have three nectaries rather than the single one of the latter species.

[4] Outside Australia it has become naturalised in South Africa where it is considered an invasive alien plant and is uprooted to prevent water depletion and protect local flora, Tanzania, Italy, Portugal, Sardinia, India, Indonesia and New Zealand.

[24] The gall-forming wasp Trichilogaster signiventris has been introduced in South Africa for biological control and has reduced the capacity of trees to reproduce throughout their range.

A field study across Australia and South Africa found that the microbes are genetically diverse, belonging to various strains of the species Bradyrhizobium japonicum and genus Burkholderia in both countries.

[37] Trichilogaster wasps form galls in the flowerheads, disrupting seed set[38] and Acizzia acaciaepycnanthae, a psyllid, sucks sap from the leaves.

[39] Acacia pycnantha is a host to rust fungus species in the genus Uromycladium that affect the phyllodes and branches.

These include Uromycladium simplex that forms pustules and U. tepperianum that causes large swollen brown to black galls, which eventually lead to the death of the host plant.

[40][41] Two fungal species have been isolated from leaf spots on A. pycnantha: Seimatosporium arbuti, which is found on a wide range of plant hosts, and Monochaetia lutea.

[43] The species has a degree of frost tolerance and is adaptable to a wide range of soil conditions, but it prefers good drainage.

[50] This was proclaimed by governor-general Sir Ninian Stephen (on the advice of the Hawke government) in the Commonwealth gazette published on 1 September.

[51] The day was marked by a ceremony at the Australian National Botanic Gardens, which included the planting of a golden wattle by Hazel Hawke, the prime minister's wife.

In 1970, a 5c stamp labelled "Golden Wattle" was issued to complement an earlier set depicting the floral emblems of Australia.

[53] The 1970 Monty Python's Flying Circus Bruces sketch includes a reference, by one of the stereotyped Australian characters, to "the wattle" as being "the emblem of our land", with suggested methods of display, including "stick[ing] it in a bottle or hold[ing] it in your hand" — despite the wattle prop itself being a large, forked branch with sparse patches of leaves and generic yellow flowers.