A shrub or small tree with green zig-zagging branches. Its long, strap-like, compound or twice-compound leaves initially have large numbers of tiny oval leaflets. These leaves are drooping in nature and have a pair of spines (5-20 mm long) at their bases. Its bright yellow flowers (2-3 cm across) have five petals and are arranged in loose elongated clusters. Its pale brown, elongated, pods are swollen around each of the seeds.
This species is scattered throughout most of northern and central Australia, except for the wettest and most arid locations. It is particularly troublesome in inland central and northern Queensland, and in the northern parts of Western Australia and the Northern Territory. Also present in the southern parts of these states, as well as in the inland parts of northern New South Wales and some parts of South Australia. Also naturalised overseas in tropical and southern Africa, Pakistan, Oceania (i.e. Hawaii and New Caledonia), and beyond its native range in the USA, Central America and Southern America.
Parkinsonia (Parkinsonia aculeata) is mostly found growing near creeks, rivers and man-made water points (i.e. bores and dams) in semi-arid regions (especially those that have a distinctive wet and dry season). It is also found in tropical and sub-tropical environments and inhabits grasslands, open woodlands, rangelands, pastures, waste areas, disturbed sites and roadsides.
An upright (i.e. erect) spiny shrub or small tree often forming dense thickets. It can reach up to 10 m tall, but usually grows 2-6 m in height.
Parkinsonia (Parkinsonia aculeata) is regarded as a significant environmental weed in Queensland, the Northern Territory and Western Australia, and as an environmental weed in New South Wales and South Australia. It is one of the 20 Weeds of National Significance (WoNS), and is actively managed by community groups in Queensland and the Northern Territory.
The branches are green in colour, hairless (i.e. glabrous), and are often drooping (i.e. pendulous) or have a zig-zagging appearance. Younger stems have a pair of sharp spines (3-20 mm long) below each leaf (i.e. stipular spines) and these remain on older stems after the leaves have been shed. Younger plants have compound (i.e. pinnate) leaves, but as the plant grows they become twice-compound (i.e. bi-pinnate) in nature. These leaves are alternately arranged along the stems, shortly stalked or almost sessile (i.e. petiolate or sub-sessile), and drooping (i.e. pendulous) in nature. Each of the twice-compound (i.e. bi-pinnate) leaves is divided into one to three pairs of long (20-40 cm), flattened, strap-like branchlets (i.e. pinnae). Numerous small, hairless (i.e. glabrous), leaflets (i.e. pinnules) are borne along these branchlets (i.e. pinnae). These leaflets (1-10 mm long and 1-2 mm wide, but mostly only 1-4 mm long) are oblong in shape and are readily shed (i.e. caducous) leaving only the long, green, drooping branchlets remaining on the plant.
The flowers (2-3 cm across) are arranged in loose elongated clusters (5-20 cm long) arising from the leaf forks (i.e. in axillary racemes). Each of these flower clusters usually contains 8-17 flowers, but the flowers can occasionally be borne singly. The flowers are bright yellow in colour, sometimes with a hint of orange or red in the centre, and are borne on slender stalks (i.e. pedicels) 5-20 mm long. They have five reddish-yellow sepals (4-8 mm long) that are fused together at the base (i.e. into a calyx tube), five petals (6-18 mm long) and ten stamens (about 6 mm long). Flowering occurs mostly during winter and spring, but larger trees may flower throughout the year. The fruit is an elongated pod that is swollen around each of the seeds (i.e. they are torulose). These pods (3-13 cm long and 5-10 mm wide) turn a light brown or straw colour when mature and usually contain 1-6 seeds (occasionally up to eight seeds). The relatively large seeds (9-15 mm long and 3-6 mm wide) are olive green to brownish in colour and are sometimes mottled. They are hard, smooth in texture, and somewhat oval (i.e. ellipsoid-ovoid) or oblong in shape.
This plant reproduces mainly by seed, but it can also produce suckers (particularly after it has been damaged).The seeds are mostly spread after being eaten by birds and other animals (e.g. cattle). The pods also float in water and the seeds can be dispersed in mud that becomes attached to animals and vehicles.
Parkinsonia (Parkinsonia aculeata) can be confused with several other thorny bushes, including prickly acacia (Acacia nilotica subsp. indica), mimosa bush (Acacia farnesiana) and the mesquites (Prosopis spp.). These species are all relatively common and widespread, and all have spines, compound leaves, yellow flowers and elongated seed pods. However, they can be distinguished by the following differences: parkinsonia (Parkinsonia aculeata) is a thorny plant with compound (i.e. pinnate) or twice-compound (i.e. bi-pinnate) leaves having few (1-3) pairs of strap-like branchlets. Its bright yellow flowers (about 2 cm across) have five petals and are borne in loose elongated clusters (i.e. racemes). The large fruit are somewhat elongated in shape (3-13 cm long and about 7 mm wide), almost cylindrical, strongly constricted between the seeds (i.e. torulose), hairless (i.e. glabrous), and turn light brown as they mature.prickly acacia (Acacia nilotica subsp. indica ) is a thorny plant with twice-compound (i.e. bi-pinnate) leaves having several to numerous (3-10) pairs of branchlets. Its fluffy bright yellow flowers are borne in small globular clusters (10-12 mm across) in the leaf forks. The large fruit are elongated in shape (6-25 cm long and 4-17 mm wide), somewhat flattened, softly hairy (i.e. pubescent), strongly constricted between the seeds (i.e. torulose), and turn greyish-green as they mature.mimosa bush (Acacia farnesiana ) is a thorny plant with twice-compound (i.e. bi-pinnate) leaves having few (2-4) pairs of branchlets. Its fluffy bright yellow flowers are borne in small globular clusters (11-15 mm across) in the leaf forks. The large fruit are somewhat elongated in shape (5-7 cm x 12-15 mm in size), almost cylindrical, often slightly curved, hairless (i.e. glabrous), and turn dark brown as they mature.the mesquites (Prosopis spp.) are thorny plants with twice-compound (i.e. bi-pinnate) leaves having few (1-5) pairs of branchlets. Its fluffy pale yellow, yellow, greenish-yellow or whitish coloured flowers are borne in dense elongated clusters (5-14 cm long) in the leaf forks. The large fruit are very elongated in shape (8-20 cm long and 7-15 mm wide), almost cylindrical, have slight constrictions between each of the seeds, and turn yellowish as they mature.