Of the 21 000+ species in the Asteraceae, the genus Erigeron contains somewhere between two hundred species (source: Wikipedia) and nearly four hundred (source: Jepson Manual). It is well represented; with ~1300 genera, the average number of species/genus in the family is roughly 16 (as an aside, this prompts the question: what are the genera in the Asteraceae with the most species?). With such diversity, it comes as no surprise that the Asteraceae are the spiders of the plant world; with a cosmopolitan distribution, you’d find it difficult to take a short walk anywhere without encountering one, except for central Greenland, Antarctica and places devoid of plant life.
The species Erigeron peregrinus is found in western North America and eastern Asia, though the particular subspecies illustrated today does not occur in Asia or northern Canada. Paul Slichter shares a description and more photographs of subalpine daisy or foreign erigeron via his site on fleabanes found east of the Cascade Mountain crest.