Conyza canadensis
Conyza floribunda
Canadian fleabane, Canadian horseweed, horseweed, vergerette du Canada
asthmaweed
faces usually glabrate (proximal margins ± ciliolate, hairs usually stiff, spreading and hispid on nerves, hairs erect);
proximal blades oblanceolate to linear, 20–50(–100+) × 4–10(–15+) mm, toothed to entire;
distal similar, smaller, 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.
3–4 mm.
3–4 mm.
1–1.5(–3) mm diam. in fruit.
1–2+ mm diam. in fruit.
20–30(–45+);
corollas ± equaling or surpassing styles, laminae 0.3–1 mm.
30–40+;
corollas ± equaling or surpassing styles, laminae 0 or to 0.3 mm.
8–30+.
10–20+.
usually glabrous, sometimes sparsely strigose (margins chartaceous to scarious);
outer greenish to stramineous, lanceolate to linear, shorter;
inner stramineous to reddish, lance-attenuate to linear.
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, sometimes corymbiform arrays.
in paniculiform or corymbiform arrays.
uniformly pale tan to light gray-brown, 1–1.5 mm, faces sparsely strigillose;
pappi of 15–25, white bristles 2–3 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.
= 18.
= 18; 54 or 56.
Conyza canadensis
Conyza floribunda
Conyza canadensis is thought to be native to North America and is now widely adventive, e.g., in South America, Europe, Asia, and Africa. Plants with stems glabrous and phyllaries red-tipped are sometimes treated as var. pusilla; similar plants with stems glabrous and phyllaries stramineous (not red-tipped) are sometimes treated as var. glabrata.
(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.)
- Local floras:
BC, 
CA, 
OR, 
WA - Local Web sites: CalFlora, CalPhotos,
Flora NW, 
IL Wildflowers, 
KS Wildflowers, 
LA Plants, 
MD Biodiversity, 
MI Flora, 
MN Wildflowers, 
MO Plants, 
PNW Herbaria, Turner Photog. 
WildflowerSearch
iNaturalist (observations)
USDA Plants Database- LBJ Wildflower Center
- SEINet
- Plants of the World Online
- Encyclopedia of Life
- Wikipedia
- Google Image Search
