Greek acantha — a thorn, sperma — seed, referring to the spiny involucral bracts enclosing the achenes.

Annual herbs. Stems erect, ascending or prostrate. Leaves along stems, opposite, nearly entire to deeply divided. Capitula radiate, solitary in leaf axils, with or without stalks. Involucral bracts in 2 rows, inner becoming woody and enlarging to enclose an achene, spiny. Receptacle with scales, conical. Ray florets female, ligulate. Disk florets functionally male, tubular. Achenes oblong. Pappus absent.

Spiny, enlarged involucral bracts, each enclosing an achene.

6 species from C and S America.

Blake (1921).

Source: Jeanes, J. (2002). Asteraceae. In: Spencer, R.. Horticultural Flora of South-eastern Australia. Volume 4. Flowering plants. Dicotyledons. Part 3. The identification of garden and cultivated plants. University of New South Wales Press.