Description: Annual herbs, pubescent.
Leaves opposite, sometimes alternate above, sessile or petiolate, ± entire to pinnatifid.
Heads solitary, axillary, sessile or on short peduncle; involucral bracts 2-seriate, elliptic to ovate, herbaceous, outer bracts 4–6, inner larger, as many as rays, ± prickly or spiny, enclosing the ray achenes and ripening with them into a burr; receptacle small, conical, with scales. Ray florets 5–8, in 1 row, female, fertile; ligules minute, emarginate or 3-toothed. Disc florets 5–30, bisexual, 5-toothed.
Ray achenes compressed parallel to a radius of the head, cuneate or oblong-fusiform, prickly, glabrous; pappus absent.
Distribution and occurrence: World: c. 8 species, tropical America, Galapagos Is. Australia: 2 species (naturalized), Qld, N.S.W., N.T.
Text by L. Murray
Taxon concept:
| | Key to the species | |
| 1 | Achenes with hooked spines of more or less uniform length; leaves usually 1.5–2.5 cm long | Acanthospermum australe |
| Achenes with hooked spines and 2 large divergent spines at apex; leaves usually 2–12.5 cm long | Acanthospermum hispidum |
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