Shrub or tree, usually 3–8 m high; branchlets glabrous, sometimes pruinose. Phyllodes often pendulous, falcate to oblanceolate or sometimes obovate, much narrowed at base, usually 9–15 cm long and 10–35(–55) mm wide, coriaceous, glabrous, obtuse to acute; pinnately veined, midrib prominent; gland often slightly exserted, sometimes 2 (rarely 3), the lowermost 3–45 mm above pulvinus; pulvinus 4–7 mm long. Raceme with rachis 2.5–9 cm long, stout, glabrous; peduncles 3–6 mm long, stout, glabrous; heads showy, globular to obloid, densely 40–80-flowered (rarely fewer), bright golden, sometimes lemon-yellow; bracteoles evident in buds, lamina subcircular, less than 0.5 mm diam., dark brown to blackish, white-fimbriate. Flowers 5-merous; sepals united. Pods linear, 5–13 cm long, 5–7 mm wide, firmly chartaceous to thinly coriaceous, glabrous; seeds longitudinal, more or less oblong, 5.5–6 mm long, somewhat shiny, black, aril clavate. Flowers Aug.–Oct.
LoM, MuM, Wim, GleP, Brid, VVP, VRiv, MuF, GipP, OtP, WaP, Gold, CVU, GGr, DunT, NIS, EGL, EGU, HSF, HNF, OtR, Strz, MonT, VAlp. Also SA, NSW, ACT; naturalised in WA, Tas. South Africa. Widespread and often locally common, growing in sand or loam in Eucalyptus forest or woodland, open-scrub and heath.
Similar to A. obliquinervia and A. saligna, but characterized by phyllodes tapering at base to a long pulvinus, with gland well-separated from pulvinus, and with a more or less central midrib; and inflorescences with stout rachises and peduncles, bearing heads with usually more than 40 flowers.
There is considerable variation within this species. Although usually a tall shrub or tree, some specimens are small and spindly, flowering when only 0.5–1 m high. Plants from open forests tend to have dark green shiny phyllodes and golden heads, while plants from deep sand in mallee areas have paler, dull, narrower phyllodes and paler-coloured heads. Plants with pruinose branches are scattered throughout the range.
Putative natural hybrids between A. pycnantha and A. williamsonii occurring in the Whipstick Forest near Bendigo superficially resemble A. hakeoides.
The bark is one of the richest sources of tannin in the world, although it is now rarely used commercially; the timber is tough and close-grained; the gum was eaten by Koories (see Cunningham et al. 1981).
