Conyza canadensis | Canadian Fleabane



Conservation status

Not Assessed

Native status


First reported in the wild



Invasive species - risk of Medium Impact

Irish status

Occasionally present, casual, vagrant, migratory

Introduction pathways - 1

Transport Contaminant

Introduction pathways subclass - 1

Seed contaminant

Invasive score


NAPRA Ireland risk assessed


Species Biology


Tall erect, green, annual, up to 1m in height, green leaves (Stace, 1997).


Considered a weed in its native range, it has a negative impact on species abundance and diversity when grown with species from outside its native range (Shah et al., 2014). Native species richness is inversely correlated with invasibility of Conyza spp suggesting it will have greater impacts on communities already subject to disturbance (Prieur-Richard et al., 2000).


Inland unvegetated or sparsely vegetated habitats; Regularly or recently cultivated agricultural, horticultural or domestic habitat; Constructed, industrial or other artificial habitats


Seed production is related to height of plant: a plant 40 cm tall produces about 2000 seeds, while a plant 1.5 m tall plant can produce as much as 230 000 seeds (Weaver, 2001).

Pathway and vector description

Repeatedly reintroduced as contaminants in various seed mixtures, generally found on waste ground (Reynolds, 2002).

Mechanism of impact

Competition, Disease transmission

Broad environment


Habitat description

Typically found on waste ground, roadsides, pavement edges, dunes and walls (Reynolds, 2002; Stace, 1997).

Species group


Native region

North America


World distribution(GBIF)

Irish distribution

Occasional - Infrequent casual, localised (Reynolds, 2002). Rosslare Harbour is the only site that has persistent records for this species.

Native distribution

Native to North America, found in all parts of Canada (C. candensis) except Newfoundland (Weaver, 2001).

Temporal change

Date of first record category


Fifty year date category


Records submitted to Data Centre in 2023

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How can you help

Report any sightings to the National Biodiversity Data Centre.



Reynolds, S.C.P. (2002) A catalogue of alien plants in Ireland. National Botanic Gardens. Glasnevin, Dublin. Stace, C. (1997). New Flora of the British Isles 2nd Edition. Cambridge University Press, Cambridge. Weaver, S. E. (2001). The biology of Canadian weeds. 115. Conyza canadensis. Canadian Journal of Plant Science, 81(4), 867-875. Shah, M. A., Callaway, R. M., Shah, T., Houseman, G. R., Pal, R. W., Xiao, S., Luo, W., Rosche, C., Reshi, Z.A., Khas, D.P. & Chen, S. (2014). Conyza canadensis suppresses plant diversity in its nonnative ranges but not at home: a transcontinental comparison. New Phytologist, 202(4), 1286-1296. Prieur-Richard, A. H., Lavorel, S., Grigulis, K., & Dos Santos, A. (2000). Plant community diversity and invasibility by exotics: invasion of Mediterranean old fields by Conyza bonariensis and Conyza canadensis. Ecology Letters, 3(5), 412-422.

CABI Datasheet