This genus is quite similar to the various asters, but fleabanes tend to bloom in spring and early summer, while asters are typical of the late summer and fall landscape. In our few species (not necessarily elsewhere), the rays of Erigeron are more numerous and narrower than is usual in the asters, while the plants tend to be lower and fewer-leaved than in most asters. Thus, in this region, the genus can be more easily recognized than might be supposed. To determine the width of the rays, it is necessary to examine flat ones (well pressed if dried), for the margins curl inward as they shrivel, and such rays appear excessively narrow.
1. Cauline leaves broadly rounded at base, sessile and usually ± clasping; heads ca. 1.5–3.5 cm broad.
2. Rays less than 0.5 mm broad; heads usually 3–30 (–40) per stem.
2. Rays (when not withered) ca. 0.8–1.7 mm broad; heads 1–4 per stem.
1. Cauline leaves tapered to a non-clasping base; heads (if radiate) mostly ca. (1–) 1.5–2.2 cm broad.
3. Plants scapose (the heads solitary on stalks naked or nearly so) and becoming stoloniferous at the base; pubescence appressed on leaves and stems.
3. Plants with leafy stems, not stoloniferous; pubescence various.
4. Rays inconspicuous, exceeding the pappus by less than 2 mm; pubescence of pedicels glandular, spreading.
4. Rays showy, longer (heads rarely discoid in E. strigosus); pubescence of pedicels antrorse, eglandular.
5. Leaves very numerous, much overlapping, linear, less than 5 mm broad, often in axillary tufts besides the principal cauline leaves; heads 1–4 (–5) per stem or main branch, on long nearly or quite naked pedicels.
5. Leaves not dense, all or mostly over 4 mm broad, with no axillary tufts; heads usually numerous (except on depauperate plants), even as many as 100 or more on robust individuals.
6. Middle region of stem glabrate to pubescent with all or many of the hairs long (0.5–1.2 mm) and spreading; principal cauline leaves usually elliptic to ovate, ca. 10–35 (–40) mm wide, with a few large teeth.
6. Middle region of stem moderately to densely pubescent with only short (0.5 mm or less) mostly appressed-antrorse hairs; principal cauline leaves linear to oblanceolate, ca. 2.5–10 (–15) mm wide, entire.