Argemone mexicana
L., Sp. Pl. 508.1753; Hook. f. & Thomson in Fl. Brit. India
1: 117. 1872.
Annuals, 30 - 125 cm high, divaricately branched, spinescent or devoid of spines (in f. leiocarpa), with yellow latex. Leaves sessile, elliptic-obovate, cordate or semi-amplexicaul at base, pinnatifid, sinuate-lobulate, 3 - 22 x 2 - 8 cm; segments inciso-dentate, acute or spiny along margins, glaucous-green with pale markings on veins, often prickly on lower surface, smooth above or on both surfaces (in f. leiocarpa). Flower buds 9 - 24 x 6 - 12 mm, sparingly or totally smooth (in f. leiocarpa); flowers bright yellow, 4 - 7 cm in diam., sessile, subtended by 2 - 3 foliaceous bracts. Sepals elliptic, 8 - 15 x 5 - 10 mm, each with 6 - 9 mm long acute terete horn, sparsely prickly outside. Petals 4 - 6, imbricate, obovate, cuneiform, crumpled in aestivation, 2 - 3 x 1.5 - 2.5 cm. Stamens many 8 - 10 mm long; filaments yellow; anthers ca 2 mm long, yellow. Ovary ovoid, 8 - 15 x 3 - 6 mm. Capsules ellipsoid to oblong, 10 - 38 x 8 - 21 mm, larger spines 4 - 9 mm long or the surface totally smooth (in f. leiocarpa); seeds many, 1.6 - 2 mm long, deeply reticulate, suborbiculate, blackish brown to deep brown.
KEY TO THE FORMAS
| 1a. Plants glabrous, devoid of any spines, except leaf margins | 1.1. leiocarpa |
| b. Plants spinescent | 1.2. mexicana |
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