notes There are various similar-looking species that share widespread distributions & weedy habit and are often difficult to separate: Erigeron canadensis, E. sumatrensis, E. florabundus, and Erigeron bonariensis. (Note that the current Jepson treatment treats E. florabundus as a synonym under E. sumatrensis.)
The (relatively!) long ray florets here (i.e. 1+ mm and clearly exceeding the phyllaries) are the clearest character placing these plants as E. canadensis per the Jepson eFlora key, FNA key...and for fun...two other keys comparing these species here (from Italy) and here (from the UK).
Per the Jepson and FNA treatments, this species is considered native to North America (and introduced in South America & elsewhere).
This was formerly placed under the genus name Conyza, for instance in the FNA treatment...but the current placement per the Jepson eFlora treatment is within genus Erigeron. More discussion of relationship of Conyza to Erigeron can be found in Nesom(1990) and Cronquist(1943).
