Symphyotrichum
Symphyotrichum () is a genus of over 100 species and naturally occurring hybrids of herbaceous annual and perennial plants in the composite family Asteraceae, most which were formerly treated within the genus "Aster". The majority are endemic to North America, but several also occur in the West Indies, Central and South America, as well as in eastern Eurasia. Several species have been introduced to Europe as garden specimens, most notably New England aster ("Symphyotrichum novae-angliae") and New York aster ("Symphyotrichum novi-belgii"). Description. Brouillet, et al. wrote: Taxonomy of "Symphyotrichum" is difficult. Species are usually heterophyllous, some strongly so . Individuals in the spring, with basal rosettes, often have leaf shapes quite different from those with cauline leaves seen later in the season. Phyllary shape on first- and later-formed heads may differ. Individuals may vary considerably in plant size and array development depending upon growing conditions. The genetic diversity within each species also appears considerable. For all species in the genus, the ray florets are white, pink, blue, or purple. Disc florets are yellow to white, becoming pinkish, reddish purple, or brown when mature. There are 5 lobes on the disc florets of all species in the genus. Taxonomy . German botanist Christian Gottfried Daniel Nees von Esenbeck established this genus in 1833 because he thought that a plant he examined, now believed to be a cultivated variety of New York aster ("Symphyotrichum novi-belgii"), which he called "Symphyotrichum unctuosum", was sufficiently distinct from the rest of the genus "Aster" to warrant its own genus. Nees emphasized the uniqueness of this plant in having its pappus hairs arranged in a coherent, basal ring. This structure is the basis for the scientific name of this genus, which derives from Ancient Greek ("sýmphysis") "growing together" and ("thríks"; stem "trich-") "hair". However, this  characteristic ring is not generally shared by most New York aster pappi, nor is it characteristic of any other plants included in the modern concept of "Symphyotrichum". Regardless, according to the rules of the International Code of Nomenclature for algae, fungi, and plants (ICN), the timing of the genus' establishment gives it precedence over other names. The genus was resurrected in 1994 by American botanist Guy L. Nesom to group together species formerly included in the genus "Aster" in order to make modern genera monophyletic. Subdivisions. "Symphyotrichum" has been divided into five subgenera: Subgenus "Ascendentes". This subgenus includes two species  from the western United States and Canada that originated as hybrids between species in the subgenera "Symphyotrichum" and "Virgulus". Subgenus "Astropolium". This subgenus includes about 10 species found across the Americas in salt marshes and salt flats. Subgenus "Chapmaniana". This subgenus includes a single species, "S. chapmanii", found in Alabama and Florida. Subgenus "Symphyotrichum". This subgenus includes about 65 species occurring across North America, including a few species in Central America and the Caribbean, with one species also occurring in Eurasia. Subgenus "Virgulus". This subgenus includes about 28 species occurring across North America, including a few species in Central America  and the Caribbean. Distribution. As a whole, "Symphyotrichum" is native throughout the Americas, with one species, "S. ciliatum", also native to eastern Eurasia. Several species have been introduced to Europe and other parts of the world. Most species are native to Mexico, the United States, and Canada, with several species occurring in the West Indies and Central America. Most members of subgenus "Astropolium" are restricted to South America. Species. , Catalogue of Life listed 106 accepted species and identified naturally-occurring hybrids, including the following: