Common Australian Garden Weeds

Argemone ochroleuca

Scientific name: Argemone ochroleuca Sweet


Habit of Mexican poppy plants (Argemone ochroleuca).


Close-up of closed flower of Mexican poppy along with leaves exhibiting a bluish-green (glaucous), almost variegated appearance.


Close-up of the deeply divided leaves of Mexican poppy with many sharp prickles.


Immature fruit of Mexican poppy, also with many prickles.


Young Mexican poppy seedling with variegated, glaucous leaves.

Common name: Mexican poppy, prickly poppy

Family: Papaveraceae

Habit:

Annual herb initially forming a rosette, then growing with upright stems to 1 m in height.

Habitat:

A weed of untended areas such as roadsides, railway lines, sandy stream beds and alluvial flats. Also found in recently cultivated paddocks.

General description:

Stems and leaves

The pithy stems are conspicuously bluish-green (glaucous) and upright. Leaves are initially arranged in a rosette and then are alternately arranged on upright stems that develop as the plant matures. The leaves are also very glaucous and are sometimes variegated in appearance. They are deeply divided (pinnatifid) with sharp prickles on the margins. Stems and leaves exude a yellowish sap when broken.

Flowers and fruits

The flower buds are oblong and 8-18 x 4 x 11 mm in size. Flowers are 3-7 cm across with six pale yellow or lemon petals. They have numerous stamens (20-75) and a purple stigma with spreading lobes exposing blue-green coloured surfaces between them. Flowering usually occurs during spring and summer. The fruit are capsules and are narrowly egg-shaped (ovoid) or ellipsoid (2-5 cm x 1-1.8 cm in size). They are spiny and may have some large recurved spines. The fruit split from the apex downward when mature. Seeds are black/brown, almost round (1.5 mm in diameter) and can be poisonous.

Distinguishing characteristics:

Annual herb developing a rosette of deeply-divided, blue-green (glaucous), leaves with sharply toothed and prickled margins. Later growing upright leafy stems which bear pale yellow six-petalled poppy flowers. There are two species with the common name of Mexican poppy. Argomone ochroleuca, which is much more common, can be differentiated from Argemone mexicana by:

its flower colour (ie. pale yellow versus bright yellow);
its bud shape (ie. oblong versus almost round in A. mexicana);
its stigmatic lobes (ie. not appressed to styles at anthesis in A. ochroleuca but are in A. mexicana.
its leaf colour (ie. conspicuously glaucous versus green or slightly glaucous in A. mexicana).

Noxious status:

Declared in Western Australia.

Sources:

Anonymous. (2000). Noxious Weed List for Australian States and Territories. National Weeds Strategy Executive Committee, Launceston.

Kleinschmidt, H.E., Holland, A. and Simpson, P. (1996). Suburban Weeds. 3rd Edition. Department of Primary Industries, Brisbane.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious Weeds of Australia. Inkata Press, Melbourne.

Stanley, T.E. and Ross, E.M. (1983-1989). Flora of South-eastern Queensland. Volume 1. Department of Primary Industries, Brisbane.