In 1994, a study of asters world-wide indicated that the native Eurasian species stand apart from the North American ones –– especially significant in this interpretation were the larger size and more symmetrically shaped chromosomes and the generally larger, 2-sided, glandular achenes of the Eurasian species.
Because the concept of the genus Aster is linked (by rules of scientific nomenclature, ICBN) to a single species –– Aster amellus, native to Europe and Asia –– the name Aster is most appropriately associated with the Eurasian species, leaving the approximately 180 North American species to find names within other genera.
Among the North American species, a number of distinct groups can be recognized –– some of them have been known for a long time. Each of these groups appears to have developed along its own evolutionary line, and the 1994 study proposed that each of the North American groups be recognized as a distinct genus.
By far the largest number of the North American species transferred from Aster to other genera are now in Symphyotrichum (about 90 species). Other North American genera where the ‘old’ asters are now located are Almutaster, Ampelaster, Aster, Canadanthus, Chloracantha, Doellingeria, Eucephalus, Eurybia, Oclemena, Oreostemma, and Sericocarpus. Aster ptarmicoides has proved to be a white-rayed species of Solidago (goldenrod).
Some of these Latinized scientific names were ‘invented’ and published long ago and, by the rules of nomenclature, must be used. The ‘principle of priority’ establishes that the first name published in a specified manner is the correct one. Symphyotrichum, which displaces the more euphonious Aster in the majority of the species, seems especially peculiar and tongue-twisting, and although it has almost never been used until very recently, it was first proposed in 1832 and can’t be denied its rightful place.
Only two North American species remain in the genus Aster, as the genus is now much more narrowly defined:
Aster alpinus –– a mountain species that crosses from Asia into Alaska and grows sporadically along the Rocky Mountains through western Canada into Colorado. The only native NA species of Aster.
Aster tataricus –– a garden species native to northeastern Asia that occasionally ‘escapes’ from cultivation in North American plantings. In states mostly east of the Mississippi River.
In retrospect, the very large genus long-recognized as Aster was identified based on a unifying concept of little more than a rhizomatous, herbaceous, perennial habit and numerous white to blue rays. This combination of features occurs in many distinct groups on both sides of the Atlantic and Pacific and it’s clear now that the evolution of Eurasian asters occurred independently of the American species.
DNA study has confirmed the basic split between the American and Eurasian species and also shown that the North American species groups are more closely related to goldenrods (Solidago), fleabanes (Erigeron), Boltonia, and other American genera than to Eurasian species of Aster. Various summaries and abstracts are available in documentation of the DNA support of these hypotheses and further reports are forthcoming, primarily from Dr. Luc Brouillet, Université de Montreal, with his students and colleagues.
Even the Eurasian species of Aster have been divided into smaller genera. Aster tripolium (the single species of the genus Tripolium), Aster sedifolius and A. punctatus (with other species, the genus Crinitaria) and Aster linosyris and A. oleifolius (with other species, the genus Galatella) are related among themselves and more closely related to Bellis, Bellium, and Bellidiastrum (= Aster bellidiastrum) than to Aster in the strict sense. The strictly defined genus Aster is now limited to A. amellus and about 180 other species native to Europe and Asia, including many beautiful ones (e.g., A. ageratoides, A. diplostephioides, A. flaccidus, A. himalaicus, A. tataricus). Among the closest relatives of A. amellus are A. pyrenaeus and A. thomsonii.
POPULAR ACCOUNTS OF THE NAME CHANGES IN ASTER
Robert Dorn. 2003. Asters Retreat to Eurasia. Castilleja 22(2): 3.
Gardener’s Notebook. 2004. Aster La Vista? The American Gardener, November-December, p. 46.
Vernon Harms. 2002. Where have all our asters gone? Blue Jay 60: 151–152.
Deborah Lewis. 2006. An Aster By Any Other Name...?: The Dismantling of the Genus Aster. Iowa Native Plant Society Newsletter, Vol. 12, Issue 3, October.
Alan Weakley. 2004. The Curious Case of the Disappearing Asters. North Carolina Botanical Garden Newsletter, March-April, p. 9.
Arthur Haines. 2001. Clarifying the generic concepts of Aster sensu lato in New England. Botanical Notes 7: 1–7.
John Semple. 2009. An Overview of “Asters.” Semple’s web site, Univ. of Waterloo, Ontario, Canada.
An excellent, easy-to-read introduction to the whole group of plants, including lots of good photos.
George Yatskievych. 2004 (2005). How faster to master the Aster disaster: a primer on the changing nomenclature of Missouri asters. Missouriensis 25: 26–32.
Brouillet, L., T. Lowrey, L. Urbatsch, V. Karaman-Castro, G. Sancho, S. Wagstaff, and J.C. Semple. 2009. Chapter 37. Phylogeny and evolution of the Astereae (Compositae or Asteraceae). Pp. 449–490. In Systematics, Evolution and Biogeography of the Compositae, Funk, V.A., A. Susanna, T. Stuessy, and R. Bayer (eds.). IAPT, Vienna, Austria.
Greuter, W. 2003. The Euro+Med treatment of Astereae (Compositae) –– generic concepts and required new names. Willdenowia 33: 45–47.
A synonymic survey of Astereae genera accepted for the purpose of the Euro+Med Project is presented.
As a consequence of shifts in generic circumscription, or reassessment of accepted specific and
subspecific taxa, combinations that are required in the genera Erigeron, Eurybia, Galatella,
Symphyotrichum and Tripolium, but do not so far exist, are validated. In one case (Erigeron alpinus
subsp. intermedius) the validity of a previous combination, even though it was rather irregularly proposed,
Nesom, G.L. 1994. Taxonomic overview of Aster sensu lato (Asteraceae: Astereae), emphasizing the New World species. Phytologia 77: 141–297.
The original publication providing detailed explanations of why North American Aster was split into the various segregate genera as well as the formalities for making the nomenclatural transfers from Aster to the segregates.
Nesom, G.L. 1995. Key to the American genera of Asterinae (Asteraceae). Phytologia 79: 281–285.
Includes an identification “key” to the North American genera segregated from Aster.
Nesom, G.L. 2000. Generic conspectus of the tribe Astereae (Asteraceae) in North America and Central America, the Antilles, and Hawaii. Sida Misc. 20: 1–100.
Semple, J.C. et al. 2001. Chromosome number determinations in fam. Compositae, tribe Astereae. VI. Western North American taxa and comments on generic treatments of North American asters. Rhodora 103: 202–218.
Semple, J.C., S.B. Heard, and L. Brouillet. 2002. Cultivated and native asters of Ontario (Compositae: Astereae): Aster L. (including Asteromoea Blume, Diplactis Raf. and Kalimeris (Cass.) Cass.), Callistephus Cass., Galatella Cass., Doelleringia Nees, Oclemena E.L. Greene, Eurybia (Cass.) S.F. Gray, Canadanthus Nesom, and Symphyotrichum Nees (including Virgulus Raf.). Univ. Waterloo Biol. Ser. 41: i–viii, 1–135.
Various authors [Geraldine Allen, Luc Brouillet, Ken Chambers, Jerry Chmielewski, Michelle Leonard, Guy Nesom, John Semple, Scott Sundberg]. 2006. Astereae (including aster segregates Almutaster, Ampelaster, Aster, Canadanthus, Chloracantha, Doellingeria, Eucephalus, Eurybia, Oclemena, Oreostemma, Sericocarpus, Symphyotrichum). Flora of North America, North of Mexico. Vol. 20.
The link here goes to the genus Aster (2 species) in Volume 20 –– each of the segregate genera is treated separately in the same volume.
John Semple’s web site. 2009. Summary of the phylogeny of the Tribe Astereae based on ITS gene sequence data. Univ. of Waterloo, Ontario, Canada.
The cladogram shows that ‘asters’ have multiple evolutionary origins.
Allen, G.A., L. Brouillet, and J.C. Semple. 2001. A molecular phylogeny of the Eucephalus asters (Asteraceae) based on ITS sequences, with biogeographic and morphological inferences. Abstract. CBA/ABC Meeting, Kelowna, BC, June 2001.
Brouillet, L., G.A. Allen, J.C. Semple, and M. Ito. 2001. ITS phylogeny of North American asters (Asteraceae: Astereae). Abstract. Botany 2001, August 2001. Albuquerque, N.M.
Brouillet, L., G.L. Nesom, A.A. Anderberg, T.K. Lowrey, and L.E. Urbatsch. 2009. Welwitschiella is a member of the African subtribe Grangeinae (Asteraceae Astereae): a new phylogenetic position based on ndhF and ITS sequence data. Kew Bull. 64(4): 1–16. Online, Dec 2009.
Fiz, O., V. Valcárcel, and P. Vargas. 2002. Phylogenetic position of Mediterranean Astereae and character evolution of daisies (Bellis, Asteraceae) inferred from nrDNA ITS sequences. Molec. Phylogenet. Evol. 25: 157–171.
Noyes, R.D. & L.H. Rieseberg. 1999. ITS sequence data support a single origin for North American Astereae (Asteraceae) and reflect deep geographic divisions in Aster s.l. Amer. J. Bot. 86: 398–412.
Selliah, S. and L. Brouillet. 2008. Molecular phylogeny of the North American eurybioid asters (Asteraceae, Astereae) based on the nuclear ribosomal internal and external transcribed spacers. Canad. J. Bot. 86: 901–915.
Vaezi, J. and L. Brouillet. 2009. Phylogenetic relationships among diploid species of Symphyotrichum (Asteraceae: Astereae) based on two nuclear markers, ITS and GAPDH. Molec. Phylogenetics Evol. 51: 540–553.
Updated 1 Jan 2010