Parkinsonia aculeata L.

Family: - Caesalpiniaceae.


Parkinsonia recognises the English botanist, John Parkinson (1567-1650).

Aculeata is Latin meaning provided with thorns and refers to the thorny habit.

Other names:

Horse Bean

Jerusalem Thorn

Pale Verde




A hairless, spiny perennial shrub or tree with zigzagged drooping branches. It grows up to 10 m tall or can have a shrub form in drier areas and form dense thickets. It has pinnate leaves with up to 100 pairs of leaflets that fall of easily leaving the main axis. Clusters of yellow flowers are produced in the leaf axils.





Very sharp spine, 5-15 mm long where the leaf joins the stem.

Oblong or parallel sided in outline. Divided twice.

The leaf consists of a long, flattened central axis that is 200-400 mm long and 2-3 mm wide and ends in a short spine. This carries 1-3 pairs of primary leaflets. On each of side of these leaflets, up to 100 pairs of oblong secondary leaflets that are 4-10 mm long occur. The primary and secondary leaflets fall off easily leaving the main axis.

Petiole - short.


Up to 10,000 mm tall, green bark, branched with stiff spines up to 12mm long on branches. Branches often slender, zig zag and drooping.

Flower head:

Loose spike like racemes, 75-150 mm long of 8-12 flowers arising from leaf axils.


Yellow and orange. Fragrant. On a long drooping stalk. 20 mm diameter.

Ovary -

Sepals -

Petals - 5 petals of which 4 are yellow, 6-15 mm long and bent back and 1 is erect with orange spots or orange-yellow.

Stamens -

Anthers -


A light brown pod, 30-150 mm long by 7 mm wide, cylindrical with a sharp point, on a short stalk. Constricted between seeds.


Oblong, dark green to brown or black. 9-10 mm long by 3-4mm wide.


Shallow taproot and many, very shallow laterals.

Key Characters:

Zig zag branches. Spiny. Yellow, 5 petalled flowers with one orange or spotted petal.


Life cycle:

Most seed germinates after the first storm for the wet season but will germinate at any time of the year. The seedling is a single thorny stem. Top growth is slow as the extensive root system develops. Plants flower in their second or third year. A flush of flowering occurs in May and June for mature plants with sporadic flowering at other times.


A very hardy plant able to grow under extreme conditions.

It tolerates a very wide range of acidities.


By seed.

Flowering times:

Any time of year.

Summer to early autumn in western NSW.

May to June mainly elsewhere.

Seed Biology and Germination:

The seed has a hard seed coat and over 99% is dormant at maturity.

Germination of seeds is improved by passage through animals, fire, scarification or acid treatment.

Germinates over a wide range of temperatures from 15-35oC.

Tolerates a wide range of acidities from pH 3-11.

Seedlings are very sensitive to water stress. There is no germination when osmotic potential are greater than 1.4 MPa.

Germination and establishment is greatest when planted at 10-70 mm deep.

Vegetative Propagules:




Population Dynamics and Dispersal:

Spread initially by intentional planting.

Now the main spread is by flood waters carrying the buoyant pods or animals eating the seeds and passing them with enhanced viability some distance away.

The seeds are large and most drop close to the parent plant.

Some spread by machinery carrying contaminated soil.

It has the potential to infest much greater areas than it now occupies.

Origin and History:

Central America. Caribbean. Mexico.

Introduced for shade and gardens in the late 1800's





Warm temperate. Semi-arid to sub-humid tropics and sub-tropics.

Prefers areas with distinct wet and dry season and those receiving run-off or supplemental water such as from bores or rivers.


Sandplains to self mulching clays.

Tolerates a wide range of soil types.

Plant Associations:




Honey plant.


A very hardy plant able to grow under extreme conditions.

Leaves eaten by sheep but generally avoided by cattle.


It can form dense thickets, blocking access to water, hindering mustering and crowding out more desirable vegetation.


Not recorded as toxic.


Noxious weed of NT, SA, WA.

Management and Control:

All spread is by seed.

Mechanical removal is effective if seedlings are controlled by cultivation and perennial pastures are encouraged to compete with it. Triclopyr is used to spot spray remnants. Basal bark and cut stump treatments using triclopyr or picloram plus 2,4D are effective on larger plants. Hexazinone granules are also effective.


Eradication strategies:

Mechanically remove old plants and burn on site. Control seedlings by cultivation in the first few years to encourage germination of dormant seed. Plant grass species and use residual herbicides to keep the area clean.

Herbicide resistance:

Biological Control:

Biological control agents are under evaluation.

Related plants:


Plants of similar appearance:


A.P.B. Advisory Leaflet No. 37 (1978)

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P382.

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P124. Photo.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #933.1.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P461-463. Photos.


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