Mexican poppy is poisonous to stock, but few deaths occur because the plant is not readily eaten. This is due to the bitter yellow sap which makes it unpalatable to stock.
Mexican poppy grows up to one metre in height. It has typical poppy flowers, hollow stems and a ‘pepper shaker’ seed capsule. Prior to flowering it resembles a thistle because of its toothed and prickly leaves.
The plant is bluish-green or greyish-green in colour. The upper surface of the leaf is smooth while the underside has a few prickles along the midribs.
The flowers are about 6cm across. They have four light yellow or cream petals surrounding a dark red, three or six-lobed stigma. After fertilisation, a prickly oblong seed capsule develops. This is up to 3.5 centimetres in length with three to six openings at the top. Each capsule contains up to 400 seeds which are round, blackish brown, and about one millimetre in diameter