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Flower (Photo: Australian Department of Agriculture and Food)
Fruit (Photo: Gareth Bain - photo in public domain)
Argemone mexicana var. ochroleuca (Sweet) Lindl.; Argemone ochroleuca var. stenophylla (Prain) Shinners
Mexican poppy, prickly poppy, devil's fig, golden thistle of Peru, biniguy thistle, white thistle, yellow poppy, Mexican thistle, Mexican prickle poppy
Native to tropical America but its exact native range is disputed
Argemone ochroleuca is invasive in parts of Tanzania (Henderson 2002) and is present in Kenya and Uganda (A.B.R. Witt pers. obs.).
Argemone ochroleuca is commonly found as a weed of roadsides, mining dumps, rabbit warrens, recently cultivated paddocks, degraded land, and over-grazed pastures. It often occurs as dense stands in sandy stream beds and alluvial flats associated with intermittent inland streams.
A glaucous (blue-green) erect single to several stemmed annual with yellow sap, reproducing only by seed and with a central taproot. It grows from 60 to 120cm in height. It has leafy stems that grow up to 60cm, with prickly lobed leaves. The flowers are showy and have a dark red 3 to 6 lobed stigma (glandular region at the tip of the style).
Stems are bluish-green, pithy, smooth or slightly pubescent (covered with short hairs). The stems grow 30 to 100cm high, with scattered stiff yellow prickles. The seed leaves are stalkless, narrow lance shaped, curved and whitish-turquoise with white veins and are about 26mm long by 1.3mm wide at the first true leaf stage. The first true leaf is narrow with three triangular, pointed lobes at the tip and a tapering base. The second true leaf is also narrow but is deeply lobed. The leaves are bluish-green and alternate. The basal leaves are slightly stalked and crowded into a dense rosette (a cluster of leaves at the base of a plant often lying flat against the ground). The upper leaves are sessile (without a stalk) and clasping the stem, the shape being variable. The leaves are generally 6 to 20cm long, 3 to 8cm wide, deeply divided into 7 to 11 coarse irregular lobes, covered with a powdery bloom; the upper surface of the leaf has paler stripes along the veins. The margin (edge) of the leaf has wavy prickles at the tips of the lobes as well as scattered on the underside of the leaf.
Flowers are creamy white to yellow, on a short stalk or sessile (without a stalk) at the ends of branches, and are 3 to 6cm wide in diameter. There are 3 hood-like sepals that are sparsely prickled with a large spine just below the apex. The sepals are shed as the flower opens. There are 6 delicate deciduous petals that are 2.5 to 3cm long and 1.4 to 4cm wide. There are numerous stamens. The sepals are shed as the flower opens. The fruit is a prickly ellipsoid capsule that is 2.5cm to 5cm long and 2cm in diameter crowned with a persistent style and narrowed at both ends and widest below the middle. When the fruit is ripe it opens from the apex downwards, splitting away from the style with ribs attached to the stigma and so resembling the ribs of an umbrella. The seeds are numerous dark brown or black and globular and are about 1.5mm in diameter.
This species reproduces by seed. Most seeds fall around the parent plant but some are dispersed by water, mud adhering to boots and farming machinery and livestock. The seeds can also be dispersed by birds. This species can be spread as a contaminant of crop grains/seeds.
Argemone mexicana, A. ochroleuca, and A. subfusiformis are often confused.
From the CABI Crop Compendium (data sheet for Argemone mexicana): 'Argemone ochroleuca (A. mexicana forma ochroleuca) has creamy white to yellow petals, an ellipsoid capsule narrowed at both ends, seeds approximately 1.5 mm in diameter. Ownbey (1997) differentiates it from A. mexicana on the basis of differences in flower bud shape and petal colour. Chaturvedi et al. (1999) have suggested that it can naturally hybridise with A. mexicana. In Zimbabwe, these two species are viewed as colour forms of one species A. mexicana (Hyde and Wursten, 2002).
A. subfusiformis is closely related to A. ochroleuca. It has cream to pale yellow petals, capsule slenderly spindle-shaped and seed approximately 2 mm in diameter. A subspecies, A. subfusiformis ssp. subfusiformis, with deep yellow flowers.
Though it has been spread widely as a contaminant, Argemone ochroleuca can be used as an ornamental plant However, this use cannot compensate for this plant's overall negative impacts.
A. ochroleuca has been listed as noxious weed in South Africa (prohibited plants that must be controlled. They serve no economic purpose and possess characteristics that are harmful to humans, animals or the environment) and in the States of Western Australia.
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. As Argemone ochroleuca is so widespread this is unlikely to be possible in many instances.
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.
Regular and timely weeding will encourage dominance of desirable species. Hand weeding of A. ochroleuca is possible but it can be painful. Weeding should be carried out before the plant has set seed. Light tillage can destroy seedlings. Spraying with a suitable herbicide can control A. ochroleuca. When using any herbicide always read the label first and follow all instructions and safety requirements. If in doubt consult an expert.
Management of grazing levels is likely to reduce susceptibility to A. ochroleuca infestations.
A biological control programme for A. ochroleuca and the closely related Argemone mexicana has been initiated in Australia (Prota database).
Not listed as a noxious weed by the state or governments in Kenya, Tanzania and Uganda.
CABI Crop Compendium online data sheet. Argemone mexicana (Mexican poppy). CABI Publishing 2011. www.cabi.org/CPC. 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.
Henderson, L. (2002). Problem plants in Ngorongoro Conservation Area. Final Report to the NCAA.
PROTA database. Prota 11(1): Medicinal plants/Plantes médicinales 1. Record display: Argemone mexicana L. database.prota.org/PROTAhtml/Argemone%20mexicana_En.htm. Accessed January 2011.
Weber E (2003) Invasive plant species of the world: A reference guide to environmental weeds. CABI publishing: United States.
Wilson, S. (1997). Some plants are poisonous. Reed Books Australia: Victoria.
Wilson B, Hawton D and Duff AA (1995) Crop weeds of northern Australia. Manager Publishing Services, Brisbane.
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]