Trees or shrubs, sometimes climbing, armed with thorns (native spp.) or unarmed (introduced spp.). Leaves alternate,
2-pinnate or (in some introduced spp.) modified to phyllodes and thus appearing to have simple leaves. Pinnae opposite,
subopposite, sometimes alternate. Gland usually present on the upper side of the petiole, sometimes also glands on the rhachis. Inflorescences usually axillary, racemose or paniculate; flowers in elongated spikes or spherical heads, bisexual or unisexual.
Calyx gamosepalous, subtruncate or with 4-5 lobes. Corolla 4-5(-7)-lobed. Stamens numerous. Anthers glandular or eglandular.
Pod very variable, dehiscent or indehiscent. An important genus, occurring commonly in a wide range of habitats. A careful distinction should be made between the stipules which in some species
are modified into straight spines arising from near the leaf base and prickles, which are usually curved
and are usually found near the nodes but may occur along the
Some acacias, especially older
trees, may be unarmed, which can be very puzzling. It is
recommended that a careful search is made of the tree (if
possible) or of similar trees in the area.
An important general rule with acacias is that those with straight spines (stipules) have flowers in spherical heads
and those with curved prickles have flowers in spikes.
The exceptions are:
Faidherbia albida has straight spines and flowers in spikes.
Acacia mellifera has curved prickles but the flower spike is so short as to appear almost spherical.
Acacia schweinfurthii has curved prickles and flowers in spherical heads.
Acacia tortilis has both curved prickles and straight spiny stipules and flowers in spherical heads.
Worldwide: 1200 species in tropical and warm areas, many in AustraliaThe larvae of the following species of insect eat species of this genus: