This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
[Caenotus Raf. Fl. Tell. 2: 50. 1836.]
Annual or biennial herbs, with small racemose thyrsoid or panicled heads of white flowers, the rays small, usually shorter than the diameter of the disk, or none. Involucre mostly campanulate, its narrow bracts in 2 or 3 series. Receptacle naked. Ray-flowers pistillate; disk-flowers perfect, their corollas usually 4-lobed or 4-toothed, the anthers obtuse at the base; style-branches somewhat flattened, their appendages short. Achenes flattened. Pappus of numerous simple fragile bristles in 1 series. [Greek, referring to the small heads.]
About 20 species, natives of America and Asia. Besides the following, 2 or 3 others occur in the southwestern United States and one is naturalized from Asia on the southern Atlantic and Pacific coast. Type species: Leptilon divaricatum (Michx.) Raf.
Erigeron canadensis L. Sp. Pl. 863. 1753.
Leptilon canadense Britton, in Britt. & Brown, 111. Fl. 3: 391. 1898.
Stem hispid-pubescent or glabrate, 3'-10° high, the larger plants paniculately much branched. Leaves usually pubescent or ciliate, the basal and lower spatulate, petioled, incised, dentate or entire, 1'-4' long, obtuse or acutish, those of the stem linear and mainly entire; heads usually very numerous; about 2" broad; involucre campanulate, 1"-1 1/2" high, its bracts linear, acute, glabrate, the outer shorter; rays numerous, white, shorter than the pappus and mostly shorter than their tubes.
In fields and waste places, a common weed throughout North America except the extreme north. Widely distributed as a weed in the Old World, the West Indies and South America. Butter-weed. Prideweed. Fireweed. Blood-staunch. Cow's-, mare's- or colt's-tail. Hogweed. Bitter-weed. June-Nov.
Erigeron divaricatus Michx. Fl. Bor. Am. 2: 123. 1803.
Leptilon divaricatum Raf. Am. Month. Mag. 2: 268. 1818.
Stem diffusely much branched, 3-12' high, pubescent or hirsute. Leaves all linear or subulate, entire, 4"-12" long, about 1/2" wide, the uppermost minute; heads numerous, about 2" broad; involucre campanulate, 1" high, its bracts linear, acute, pubescent, the outer shorter; rays purplish, shorter than their tubes.
In sandy soil, especially along rivers, Indiana to Minnesota, Tennessee, Louisiana, Nebraska and Texas. June-Oct.