Click on images to enlarge
flower clusters and leaves (Photo: Land Protection, QDNRW)
flowers (Photo: Land Protection, QDNRW)
mature fruit and seeds (Photo: Land Protection, QDNRW)
close-up of small leaflets on the strap-like leaves (Photo: Sheldon Navie)
greenish-coloured older stem with thorns (Photo: Sheldon Navie)
habit of younger tree (Photo: Sheldon Navie)
seedling (Photo: Sheldon Navie)
habit of mature tree (Photo: Land Protection, QDNRW)
mature fruit (Photo: Land Protection, QDNRW)
infestation (Photo: Land Protection, QDNRW)
close-up of flowers and young fruit (Photo: Land Protection, QDNRW)
thorns and leaves on younger stem (Photo: Sheldon Navie)
Parkinsonia thornberi M.E.Jones
Barbados flower-fence, horse bean, horse-bean, horsebean, jelly bean tree, Jerusalem thorn, Mexican paloverde, palo verde, parkinsonia, retaima, sessaban
Fabaceae (Leguminosae): subfamily Caesalpinioideae
Native to southern USA, northern Mexico, the Galapagos Islands and northern South America (Bolivia, Peru, Paraguay, Uruguay and northern Argentina).
Parkinsonia aculeata is invasive in parts of Kenya (CABI Invasive Species Compendium), present in Tanzania and naturalised in Uganda (A.B.R. Witt pers. obs.). In East Africa, it is widely cultivated and is naturalised in the dry parts of Kenya, (Wajir, Hola, Magadi, Garissa and Homa Bay. In Uganda, it is mostly grown around Kasese and the North Eastern Region. In Tanzania, it grows at high altitudes with 200 to 1000 mm of annual rainfall.
Parkinsonia aculeata is mostly found growing near creeks, rivers and man-made water points (bores and dams) in semi-arid regions (especially those that have a distinctive wet and dry season). It is also found to inhabit grasslands, open woodlands, rangelands, pastures, waste areas, disturbed sites and roadsides.
The branches are green in colour, hairless (glabrous), and are often drooping (pendulous) or have a zigzag appearance. Younger stems have a pair of sharp spines (3-20 mm long) below each leaf (stipular spines) and these remain on older stems after the leaves have been shed.
Younger plants have compound (pinnate) leaves, but as the plant grows they become twice-compound (bi-pinnate) in nature. These leaves are alternately arranged along the stems, shortly stalked or almost sessile (petiolate or sub-sessile), and drooping (pendulous) in nature. Each of the twice-compound (bi-pinnate) leaves is divided into one to three pairs of long (20-40 cm), flattened, strap-like branchlets (pinnae). Numerous small, hairless (glabrous), leaflets (pinnules) are borne along these branchlets (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 (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 (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 (pedicels) 5-20 mm long. They have five reddish-yellow sepals (4-8 mm long) that are fused together at the base (into a calyx tube), five petals (6-18 mm long) and ten stamens (about 6 mm long).
The fruit is an elongated pod that is swollen around each of the seeds (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 (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 aculeata is used for firewood, charcoal, medicine, fodder (pods and leaves)shade, mulch and as a live fence. It is useful in soil stabilisation as a windbreak.
Due to its prolific seeding, Parkinsonia aculeata can become weedy, and outcompete non shade-tolerant species. In South Africa, P. aculeata is noted as being a potential transformer species. It has been listed as a noxious weed in all Australian states.
The precise management measures adopted for any plant invasion will depend upon factors such as the terrain, the cost and availability of labour, the severity of the infestation and the presence of other invasive species. Some components of an integrated management approach are introduced below.
The best form of invasive species management is prevention. If prevention is no longer possible, it is best to treat the weed infestations when they are small to prevent them from establishing (early detection and rapid response). Controlling the weed before it seeds will reduce future problems. Control is generally best applied to the least infested areas before dense infestations are tackled. Consistent follow-up work is required for sustainable management.
Seedlings and small plants can be removed by hand though care must be taken because of the plant's thorniness. Bulldozing, and deep ploughing can be effective but must be followed up as it brings seeds to the surface. Fire can control seedlings though adult plants are not very susceptible. Herbicide application, especially as a basal bark methods (painting herbicide onto the bark) or cut stump treatment can be effective on mature trees. When using any herbicide always read the label first and follow all instructions and safety requirements. If in doubt consult an expert.
Three biological organisms have been introduced in Australia: two seed beetles (Penthobruchus germaini and Mimosestes ulkei) which attack the mature seeds, and one leaf bug (Rhinacloa callicrates) which feeds on the leaves and shoots.
Not listed as a noxious weed by the state or governments in Kenya, Tanzania and Uganda.
Germplasm Resources Information Network (GRIN). www.ars-grin.gov/npgs/index.html. National Germplasm Resources Laboratory, National Genetic Resources Program, Agricultural Research Service (ARS), United States Department of Agriculture (USDA), Beltsville, Maryland, USA. Accessed March 2011.
Global Compendium of Weeds. www.hear.org/gcw. Hawaiian Ecosystems at Risk Project. Accessed March 2011.
Henderson, L. (2001). Alien weeds and invasive plants. A complete guide to declared weeds and invaders in South Africa. Plant Protection Research Institute Handbook No. 12, 300pp. PPR, ARC South Africa.
Katende, A.B., Birnie, A. and Tegnas, B. (1995). Useful trees and shrubs for Uganda. Identification, Propagation and Management for Agricultural and Pastoral Communities. Regional Soil Conservation Unit (RSCU), Swedish International Development Authority (SIDA).
Lazarides, M., Cowley, K. and Hohnen, P. (1997). CSIRO Handbook of Australian Weeds. CSIRO Publishing, Collingwood, Victoria.
Maundu P. and Tegnas T. (eds.) (2005). Useful trees and shrubs for Kenya. Technical handbook No. 35. Nairobi, Kenya.
Mbuya, L. P. , Masanga H. P., Bernie, A. and Tegnas, B. (1994). (eds). Useful Trees and Shrubs for Tanzania. Identification, propagation and management for agricultural and pastoral communities. Regional Soil conservation Unit, Nairobi, Kenya.
Pacific Island Ecosystems at Risk (PIER). Parkinsonia aculeata L., Fabaceae (Leguminosae): plant threats to Pacific ecosystems. www.hear.org/Pier/species/parkinsonia_aculeata.htm. Institute of Pacific Islands Forestry, Hawaii, USA. Accessed March 2011.
Agnes Lusweti, National Museums of Kenya; Emily Wabuyele, National Museums of Kenya, Paul Ssegawa, Makerere University; John Mauremootoo, BioNET-INTERNATIONAL Secretariat - UK.
This fact sheet is adapted from The Environmental Weeds of Australia by Sheldon Navie and Steve Adkins, Centre for Biological Information Technology, University of Queensland. We recognise the support from the National Museums of Kenya, Tropical Pesticides Research Institute (TPRI) - Tanzania and Makerere University, Uganda. This activity was undertaken as part of the BioNET-EAFRINET UVIMA Project (Taxonomy for Development in East Africa).
BioNET-EAFRINET Regional Coordinator: [email protected]