2n = 20

Prostrate annual, 10--30 cm diam., sometimes producing adventitious roots from lower nodes, usually several-branched from base, varying from being glabrescent with a few cottony hairs on young growth, to, rarely, moderately cottony allover. Leaves ± obovate to spathulate in outline, 4-8(-12) mm long, 1.5-4 mm wide, mostly with 1-3 acute to blunt teeth along each side, rarely entire, margin slightly thickened and/or sometimes slightly recurved, resin-dotted on both surfaces, concolorous or slightly paler beneath. Inflorescence a single sessile capitulum, often leaf-opposed, immediately subtended by a leaf and appearing axillary to it, sometimes in branch-axils. Capitula at anthesis ± hemispherical, distinctly domed, 3-4(-7) mm diam., (immature capitula, prior to anthesis, cup-shaped to biconvex); involucral bracts obovate, 1-2 mm long, minutely ruminate and membranous distally; receptacle distinctly domed, hemispherical or slightly lower than this; female (outer) florets c. 60--120 in 3-5 rows, corollas narrowly cylindrical, 0.3-0.4 mm long; bisexual florets 8-16, corollas narrowly funnel-shaped, c. 0.5-0.8 mm long (including lobes 0.2-0.3 mm long and wide). Fruiting heads firm, somewhat persistent, but disintegrating before stems senesce; bracts of fruiting heads widely spreading to slightly deflexed near base, slightly upcurved in distal half, not significantly thickened and not pithy toward base; fruiting receptacle 0.9-1.3 mm diam., the underlying pith layer not extending below base of involucre; cypselas clavate or narrowly obcuneoid (less than 5 times longer than wide), 1.2-1.7 mm long, obtuse (female florets) or truncate (bisexual florets) at apex, smooth or minutely scabridulous in the lower half only, prominently and usually regularly 4-angled with prominent ribs at each of the angles, usually with a finer rib alternating with each of the major angles, the ribs terminating 2/3 or 4/5 of the cypsela length in a thickened spongy apical portion, pericarp between ribs usually thin, revealing the brown shining seed beneath, vesicular trichomes absent from cypsela body or sparsely scattered over faces, hairs antrorsely spreading or subappressed, 0.2-0.4 mm long, confined to ribs, extending from base to the distal quarter of cypsela, neither inrolled nor conspicuously thickened at apex, acute or obtuse.

a C. cunninghamii foliis minoribus, habitu prostrato, capitulis minoribus plerumque, flosculis bisexualibus paucioribus differt.