Introduced annual or perennial forb, prostrate or to 15cm tall. Leaves opposite each other, 0.5-6cm long, 6-30mm wide, flat, hairless to sparsely hairy, with straight points. Flowers yellowish green to brownish, with 5 sharp pointed 'petals', in globular to oval groups at the bases of the leaves. Fruiting bodies with many sharp points. Declared plant in SA. Noxious weed in Vic.
Description (page 282) and photo (page 283) in G.M. Cunningham, WE Mulham, PL Milthorpe and J H Leigh (1981 and later printings) Plants of Western New South Wales
Weeds of Australia Biosecurity Queensland Edition description: http://keyserver.lucidcentral.org/weeds/data/03030800-0b07-490a-8d04-0605030c0f01/media/Html/Alternanthera_pungens.htm