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Argentine fleabane, asthmaweed, flax-leaf fleabane, flax-leaf horseweed, hairy horseweed, South American conyza, wavy-leaf fleabane


Habit Plants erect, 10–100(–150+) cm, branched mostly distally. Plants erect, 30–150+ cm, branched mostly distally.

faces ± densely strigose or hispidulous;

proximal blades oblanceolate, 30–80(–120+) × 10–25+ mm, obscurely lobed to coarsely toothed or entire;

distal narrowly oblanceolate to linear, 10–50 × 2–10 mm, obscurely toothed or entire.

faces sparsely strigose to hispidulous or glabrate (margins ± ciliolate proximally, hairs erect, on nerves);

proximal narrowly oblanceolate to linear, 50–100 × 5–15 mm, toothed or entire;

distal similar, smaller, entire.


3.5–5 mm.

3–4 mm.


3–5 mm diam. in fruit.

1–2+ mm diam. in fruit.

Pistillate florets


corollas ± equaling or surpassing styles, laminae 0 or to 0.3 mm.


corollas ± equaling or surpassing styles, laminae 0 or to 0.3 mm.

Disc florets




usually strigose or hispidulous;

outer greenish to purplish, lanceolate, shorter;

inner stramineous to purplish, linear-attenuate (more chartaceous to scarious, less hairy).

usually sparsely strigose (at least the outer; margins chartaceous to scarious), outer greenish, becoming reddish brown, lanceolate, shorter, inner stramineous to reddish, lance-attenuate.


usually in paniculiform to racemiform, rarely corymbiform arrays.

in paniculiform or corymbiform arrays.


pale tan, 1–1.5 mm, faces glabrous or sparsely strigillose;

pappi of 15–25+, pinkish, sordid, or tawny bristles 3–4+ mm.

pale tan (usually some with reddish nerves), 1–1.5 mm, faces sparsely strigillose or glabrate;

pappi of 15–25 white bristles 2–3 mm.


= 54.

= 18; 54 or 56.

Conyza bonariensis

Conyza floribunda

Phenology Flowering year round, mostly late summer–fall. Flowering summer–fall.
Habitat Disturbed sites, along roads and streets Disturbed sites
Elevation 0–500 m (0–1600 ft) 10–100 m (0–300 ft)
from FNA
AL; AZ; CA; FL; GA; LA; MS; NC; NM; OR; SC; TX; UT; VA; South America [Introduced in North America]
[WildflowerSearch map]
from FNA
CA; FL; Mexico; Central America; South America; Europe; Asia; Africa [Introduced in North America]

Conyza bonariensis is widespread in tropical and warm-temperate regions of the world. It is thought to be native to South America.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Conyza floribunda is thought to be native to South America.

In some floras of the past 50 or so years, Conyza bilbaoana has been treated as distinct from C. floribunda; in others, C. bilbaoana and C. floribunda have been treated as synonyms of C. bonariensis. For some traits (e.g., indument, phyllaries, florets), members of C. floribunda are intermediate to C. bonariensis and C. canadensis; some specimens that I have called C. floribunda may be hybrids. For example, a robust specimen from Santa Cruz Island, California, was originally labeled “C. bonariensis ×canadensis (?).” Locally (e.g., in Berkeley, California), C. canadensis usually comes into flower as C. bonariensis goes to seed. So far as sampled, C. canadensis is diploid; C. bonariensis is hexaploid. Pollen stainability in the Santa Cruz Island specimen is ca. 99%.

If treated as a variety of Conyza bonariensis, the correct name for the taxon treated here as C. floribunda is C. bonariensis var. leiotheca.

Some botanists, e.g., J. B. Marshall (1974), have treated the nomenclatural types of Conyza floribunda and C. sumatrensis (Retzius) E. Walker (= Erigeron sumatrensis Retzius) as conspecific.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 20, p. 349. FNA vol. 20, p. 350.
Parent taxa Asteraceae > tribe Astereae > Conyza Asteraceae > tribe Astereae > Conyza
Sibling taxa
C. canadensis, C. floribunda, C. ramosissima
C. bonariensis, C. canadensis, C. ramosissima
Synonyms Erigeron bonariensis C. bilbaoana, C. bonariensis var. leiotheca
Name authority (Linnaeus) Cronquist: Bull. Torrey Bot. Club 70: 632. (1943) Kunth: in A. von Humboldt et al., Nov. Gen. Sp. 4(fol.): 57. (1818)
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