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.

Erect or ascending perennial (sometimes annual in adverse conditions) to c. 30 cm high, new growth commonly resprouting from base, glabrous, or cottony near the growing tips, or rarely cottony overall. Leaves oblong or narrowly obovate, 7-30 mm long, 2.5-7 mm wide, serrate, glabrous, resin-dotted on both surfaces, concolorous or slightly paler below. Inflorescence a single sessile cauline capitulum, not leaf-opposed, often in branch axils. Capitula at anthesis biconvex, hemispherical or subglobular, 4-6(-8) mm diam.; involucral bracts 3-5-seriate, obovate, 1.5-3 mm long, entire or with minutely ruminate membranous margins, glabrous to lightly (rarely densely) cottony; receptacle strongly convex; female (outer) florets c. 200-350, in 7-12 rows, corollas narrowly cylindrical, 0.3-0.5(-0.7) mm long (including lobes c. 0.1 mm long); bisexual florets c. 20-50(-70), corollas funnel-shaped, 0.7-0.8 mm long (including lobes c. 0.3 mm long and wide), pale green, rarely tipped reddish. Fruiting heads usually remaining intact until stems senesce; bracts of fruiting heads widely spreading; fruiting receptacle 1.8-2.5(-3.5) mm diam., with a pith layer entirely contained within the dome of the receptacle; cypselas oblong, 1.2-1.6 (-2) mm long, truncate or rounded at apex, with 4 prominent ribs, occasionally with 1 or 2 minor ribs, the ribs smooth or scabridulous, united at or above three-quarters of the cypsela length into a thickened, spongy or corky apical portion, the pericarp between the ribs in the lower part normally very thin with the brown testa of the seed apparent; vesicular trichomes scattered over the faces of the cypsela between the ribs. Hairs on ribs antrorse (sometimes appressed), c. 0.1-0.2 mm long, usually tightly inrolled at their apices.

Prostrate annual or perennial; branches to c. 30 cm long, sometimes rooting from lower nodes, essentially glabrous, but sometimes with short arachnoid hairs near the growing tip. Leaves mostly alternate, obovate or narrowly obovate, (6-)10-20 mm long, 2.5-8 mm wide, entire or shallowly serrate, glabrous, resin-dotted on both surfaces, concolorous or slightly paler beneath. Inflorescence a single shortly pedunculate capitulum, usually leaf-opposed; peduncle 0.5-3 mm long. Capitula at anthesis biconvex to hemispherical, 3-5 mm diam.; involucral bracts 1-2-seriate, obovate with ruminate membranous margins, 1-1.5 mm long; receptacle convex; female (outer) florets 40-80, in 2-4 rows, corollas narrowly cylindrical, 0.2-0.4 mm long (including lobes less than 0.1 mm long), green or yellow-green; bisexual (inner) florets 4-14, corollas broadly obconical, 0.5-0.7 mm long (including lobes 0.2-0.3 mm long and wide) often purplish. Fruiting heads breaking up before stems senesce, involucral bracts at fruiting widely spreading to slightly deflexed; fruiting receptacle 1.5-2 mm diam., with a pith layer entirely contained within the dome of the receptacle; cypselas of female and bisexual florets similar, narrowly obovate, 1.2-2.0 mm long, 0.5-0.8 mm wide, obtuse at apex, usually somewhat flattened, 3- or 4-angled in section, each angle with a thickened longitudinal rib, each intervening face membranous with a less prominent rib (sometimes 1 or 2 faces lacking a rib), at least the larger ribs with short ascending to appressed hairs, intervening faces with scattered glandular trichomes; pericarp slightly thickened at and shortly below the apex.

Annual or facultatively perennial herbs, glandular and aromatic. Leaves alternate, cauline, sessile, toothed to entire, glandular-punctate, glabrous to densely cottony. Inflorescences mostly terminal and solitary, but appearing axillary by sympodial growth of subtending shoots, rarely racemose or truly axillary. Capitula heterogamous, sessile to shortly pedunculate, globular, biconvex, hemispherical, cup-shaped or campanulate; involucral bracts in c. 2 rows, herbaceous, scarious-margined; receptacle slightly concave to distinctly convex, glabrous, epaleate, with pithy tissue present to some degree below surface; outer florets female, corolla tubular, narrowed above and minutely 3-lobed, lobes very short relative to tube, acute to rounded, style branches linear, glabrous; inner florets bisexual, corolla funnelform, 4-lobed, lobes triangular, from half to almost as long as tube; both corolla types with scattered short vesicular trichomes (appearing as glistening sessile resin droplets); anthers shortly tailed, lacking apical appendages, or with short ovate apical appendages, anther collar not strongly differentiated, tapering evenly from filament to anther base, c. 0.05 mm long, style branches oblong, broadly rounded and papillose apically. Cypselas of female and bisexual florets similar, clavate to cylindric, 4-6(-16)-ribbed, mostly with a swollen, pithy or spongy apical portion; glandular trichomes generally present between ribs, eglandular hairs usually present along ribs, acute and straight or tightly inrolled at the apex; pappus absent. Carpopodium absent.

Prostrate to (rarely) erect annual or facultative perennial, spreading to c. 25 cm diam. and/or 20 cm high; adventitious roots sometimes produced from lower nodes; branches glabrescent to moderately (rarely densely) cottony, if glabrescent then axils and young growing tips usually with some cottony hairs. Leaves obtrullate to spathulate, 3-12(-27) mm long, 1.5-6(-11) mm wide, variably serrate to shallowly incised; surfaces glabrescent to densely cottony, with scattered resin droplets. Inflorescence a solitary sessile or subsessile capitulum, (peduncles to c. 1 mm long), appearing axillary or leaf opposed. Capitula at anthesis hemispherical to subglobular, 1.5-5 mm diam.; involucral bracts obovate with erose membranous margins, 1-1.6 mm long; receptacle convex; corollas of female florets 0.1-0.25 mm long; corollas of bisexual florets 0.3-0.4 mm long. Fruiting heads breaking up before stems senesce. Cypselas narrowly obcuneate (length-width ratio c. 3-4), 0.6-1.5 mm long, truncate or obtusely rimmed and very slightly impressed at the apex, the 4-6(-8) ribs with short ascending bristles, uniting in the distal quarter to half into a pale, pithy apical portion, faces between ribs with vesicular trichomes in a vertical row or scattered (rarely with scattered hairs), hairs antrorsely appressed to spreading, 0.15-0.2 mm long, acute or obtuse (not inrolled or thickened) at apex.

Stems and base of capitula glabrescent to moderately cottony; leaves ± kite shaped, 3-12(-27) mm long, 1.5-6(-11) rom wide, cottony to glabrescent. Capitula at anthesis 1.5-3(-3.5) mm dlam.; involucral bracts c. 1 mm long; receptacle depressed-hemispherical, 1-1.2(-1.5) mm diam. at anthesis; female florets 75-200, corollas 0.1-0.25 mm long; bisexual florets 10-20, corollas 0.3-0.4 mm long. Cypselas narrowly obcuneate, 0.7-1.1 mm long, c. 0.3 rom wide, with scattered vesicular trichomes on faces; angles 4(-6), obtuse to acute.