Flowering plants commonly known as "asters" are members of more than a dozen genera in the tribe Astereae of the Sunflower family. Asters of all sorts occur throughout North America and across Northern and Central Eurasia, with a few species in South America. There are estimated to be some 350 species of "asters" worldwide; about 150 of them are native to Canada and/or the United States. Traditional treatments place most asters in the genus Aster L. However, during the last decade analyses of morphology, chloroplast DNA restriction fragment length polymorphisms and ITS sequence data, and on going karyotype studies have all demonstrated that asters are polyphyletic and members of a number of very distinct phylads within the tribe (Nesom 1994 and numerous cited papers); Lane et al. 1996; Xiang and Semple 1996; Noyes and Rieseberg 1999; Brouillet et al. 2001; Semple et al. 2002; Brouillet et al., 2009). To understand relationships among the different kinds of asters, one must first know the phylogeny of the entire Tribe Astereae. Asters can be divided into two categories following the general phylogeny of the entire tribe:
- "Asters" related to genera native to South America, Africa and Asian
- "Asters" of the North American clade of the tribe
The presentation here represents a significant shift in my opinion regarding generic limits from a traditional view of Aster to one that I believe will be the "new standard taxonomy" of asters. There really is no satisfactory compromise between the desire to maintain Aster as a large broadly defined genus with as many species as possible and the need to recognize that the traditional very broad concept of the genus is not monophyletic and not based on synapomorphies (shared derived traits). The treatment of asters in Semple et al. (1996) was an attempt at an acknowledged compromise between the old and new classifications and as such was inconsistent with the most recent data. Most significant is that the molecular evidence strongly shows that there are no true asters in North America (members of the genus Aster) with one exception, the arctic-alpine Aster alpinus ssp. vierhapperi (syn: Aster culminis) and that the majority of species traditionally placed in the genus Aster by North American botanists correctly belong in Eurybia Nees and Symphyotrichum Nees.
The generic treatment of North American asters proposed by Guy Nesom (1994) fit the new data quite well, although there are a number of species and a few groups of species that are not aligned in accordance with the molecular data. These are either realigned as indicated in this website or the continuing ambiguity about their phylogenetic position is discussed.
In the discussion below many of the genera cited are linked to additional pages posted on the this web site that present information on morphology, cytology and summaries of unresolved problems with phylogeny and classification. Numerous illustrations of individual species can be accessed from these additional pages.
The Tribe Astereae includes about 225 genera and 3,100 species (Chen, Chen, Brouillet & Semple 2011). This web site deals with only a small portion of these taxa.
The first category of asters and many non-aster-like Astereae are found in Africa and Southeastern Asia, New Zealand and Australia with close relatives in Europe and Asia. An early branch of the tribe reached South America as did a later branch. The genus Aster in the new monophyletic sense (type species Aster amellus) is Eurasian and is a member of this first category of Astereae. It is a middle level branch in the phylogenetic grade from the begins with the basal genus Denekia and ends with the more recently evolved second South American clade (Brouillet et al. 2009). The genus Aster includes species previously included in Asteromoea, Diplactis, Heteropappus, Kalimeris, and Rhynchospermum. The basal grade of phylads also includes some African and Eurasian "aster" and aster-like genera such as Bellis, Callistephus, Felicia, Galatella, Linosyris and Tripolium, which at one time or another have been included in Aster in the broadest polyphyletic sense. These all have a chromosome base number of x=9. Bremer (1994) hypothesized that the tribe had either paleotropical or North American origins. Semple (1995) incorrectly hypothesized that the tribe had its origins in Eurasia and that on the basis of RFLP cpDNA data genera such as Erigeron and Felicia were primitive members of the tribe, while Aster was North American and not primitive. Nesom (1994) proposed a southern hemisphere origin for the tribe. Southern Africa is the likely point of origin for the Tribe Astereae (Brouillet et al. 2009). Long distance dispersal must account for the present distribution patterns of the tribe across the southern hemisphere and from southern hemisphere areas into northern hemisphere areas. Several migrations from Africa into South America occurred at different times in the history of the tribe. Migrations out of the Southern Hemisphere into Eurasian and Australia/New Zealand occurred several times and into North America just once. Members of the North American clade much more recently migrated into Europe, Asia and South America (e.g., Erigeron and Solidago).
The North American Clade of the tribe Astereae is well defined genetically (Noyes and Rieseberg 1999; Brouillet et al. 2001, 2009). The NA Clade includes various kinds of asters, the goldenrods (Solidago and related genera Brintonia, Chrysoma, Chrysothamnus, Oreochrysum, Petradoria; subtribe Solidagininae group I), the grass-leaved goldenrods (Euthamia; Solidagininae group II), fleabanes (Erigeron; subtribe Conyzinae), goldenasters (Bradburia, Chrysopsis, Heterotheca, Pityopsis; subtribe Chrysopsidinae), and many other genera of white, purple and yellow rayed or rayless flowering herbs and shrubs (e.g., Arida, Corethrogyne, Dieteria, Grindelia, Haplopappus in the narrow sense, Hazardia, Isocoma, Machaeranthera, Pyrrocoma, Rayjacksonia, Xanthisma in the broad sense, Xylorhiza; substribe Machaerantherinae: and Ericameria; subtribe Pentachaetinae)
The NA Clade includes some 13 genera of "asters" which sometimes occupy a basal position in several different main branches of the clade. These include Doellingeria, Eucephalus, Eurybia, Herrickia, Ionactis, Oclemena, Oreostemma, Sericocarpus and Subtribe Symphyotrichinae, which is divided on molecular and morphological grounds into Canadanthus, Ampelaster, Almutaster, Psilactis and Symphyotrichum (including Brachyactis and Virgulus). Brouillet et al. (2001) and Brouillet et al. (2004, 2009) included sufficient species to adequately resolve the phylogenetic position of each of these genera within the North American Clade. Previous studies lacked sufficient numbers of "asters" to achieve this, although members of some were included in DNA studies (Xiang and Semple 1996; Noyes and Rieseberg 1999). Nesom's studies (2000, 1996 and earlier) give an overview of the morphological limits of these native North American genera of asters with some modifications noted on this web site. Revised treatments of all of these aster genera are presented in Flora of North America. Vol. 20. Asteraceae, Part 2. Astereae and Senecioneae (Oxford University Press).
Publications on asters by John C. Semple
Semple, J.C. 1976. The karyotype of Aster ericoides L. (Asteraceae): some Canadian populations. Canad. J. Genet. Cytol. 18: 661-664.
Semple, J.C. 1978. The cytogeogrpahy of Aster pilosus (Compositae-Astereae): Ontario and the adjacent United States. Canad. J. Bot. 56: 1274-1279.
Semple, J.C. 1979. The cytogeography of Aster lanceolatus (synonyms A. simplex and A. paniculatus) in Ontario with additional counts from populations in the United States. Canad. J. Bot. 57: 397-402.
Semple, J.C. and L. Brouillet. 1980a. A synopsis of North American asters: the subgenera, sections and subsections of Aster and Lasallea. Amer. J. Bot. 1010-1026.
Semple, J.C. and L. Brouillet. 1980b. Chromosome numbers and satellite chromosome morphology in Aster and Lasallea. Amer. J. Bot. 67: 1027-1039.
Semple, J.C. and J. Ford. 1981. The phytogeography of leaf morphology in two species of North American asters: Lasallea novae-angliae and L. oblongifolia (Compositae). Brittonia 35: 517-522. [Lasallea = Virgulus]
Semple, J.C. 1982. Observations on the morphology and cytology of Aster hemisphaericus, A. paludosus and A. chapmanii with comments on the chromosomal base number and phylogeny of Aster subg. Aster sect. Heleastrum. Syst. Bot. 7: 60-70.
Semple, J.C. and R. A. Brammall. 1982. Wild Aster lanceolatus × lateriflorus hybrids in Ontario and comments on the origin of A. ontarionis (Compositae: Astereae). Canad. J. Bot. 60: 1895-1906.
Semple, J.C. 1982b. Aster avitus in North Carolina. Castanea 47: 409-410.
Semple, J.C., J.G. Chmielewski, K. S. Rao & G. A. Allen. 1983. The cytogeography of Aster lanceolatus. II. A preliminary survey of the range including A. hesperius. Canad. J. Bot. 61: 434-441.
Chmielewski, J.G. and J.C. Semple. 1983. The cytogeography of Aster lanceolatus. III. Cytoecology in southern Ontario. Canad. J. Bot. 61: 1879-1886.
Semple, J.C., J.G. Chmielewskiand C.C. Chinnappa. 1983. Chromosome number determinations in Aster L. (Compositae with comments on cytogeography, phylogeny and chromosome morphology. Amer. J. Bot. 70: 1432-1443.
Semple, J.C. and J.G. Chmielewski. 1983. Treatment of Aster. In: G.W. Argus and D.J. White, eds. Atlas of the rare vascular plants of Ontario. Part 2. National Museums of Canada, Ottawa.
Semple, J.C. 1984. Cytogeographic studies on North American asters. I. range surveys of Virgulus adnatus, V. concolor, V. georgianus, V. grandiflorus, V. novae-angliae, V. ob- longifolius, V. patens, and V. walteri. Amer. J. Bot. 71: 522-531.
Semple, J.C. and J.G. Chmielewski. 1985. The cytogeography of Aster pilosus (Compositae- Astereae). II. Survey of the range, with notes on A. depauperatus, A. parviceps and A. porteri. Rhodora 87: 367-379.
Chmielewski, J.G. and J.C. Semple. 1985. Cytogeographic studies on North American asters. II. Virgulus ericoides and V. novae-angliae in southern Ontario. Canad. J. Bot. 63: 1652-1653.
Semple, J.C. 1985a. Chromosome number determinations in Fam. Compositae tribe Astereae. Rhodora 87: 517-527.
Semple, J.C. 1985b. New names and combinations in Astereae. Phytologia 58: 429-431.
Chmielewski, J.G. and J.C. Semple. 1985 . Significant range extension series: Aster praealtus var. praealtus new to Perth County. Ontario Field Biol. 38 : 37.
Semple, J.C. and J.G. Chmielewski. 1987a. A revision of the Aster lanceolatus Complex (Compositae: Astereae): a multivariate morphometric study. Canad. J. Bot. 65: 1046-1062.
Semple, J.C. and S. B. Heard. 1987. The asters of Ontario: Aster L. and Virgulus Raf. (Compositae: Astereae). Univ. Waterloo Biol. Ser. 30: 1-88.
Semple, J.C. and J.G. Chmielewski. 1987b. Chromosome numbers in Fam. Compositae, Tribe Astereae. II. Additional Counts. Rhodora 89: 319-325.
Semple, J.C. and J. G. Chmielewski, and M. Lane. 1989. Chromosome numbers in Fam. Compositae, Tribe Astereae. III. Additional counts and comments on some generic limits and ancestral base numbers. Rhodora 91: 296-314.
Chmielewski, J.G., and J.C. Semple. 1989. The cytogeography of Aster pilosus var. pilosus in southern Ontario revisited. Canad. J. Bot. 67: 3517-3519.
Semple, J.C. and J.G. Chmielewski. 1991. A multivariate morphometric study and revision of Aster subg. Doellingeria sect. Triplopappus (Compositae: Astereae). Canad. J. Bot. 69: 256-276.
Semple, J.C. 1992. A geographic summary of chromosome number reports for North American asters and goldenrods (Compositae: Astereae). Ann. Missouri Bot. Garden 79: 95-109. [Based on invited paper presented at the W.H. Lewis Tribute Symposium, St. Louis, 7 Oct 1990]
Semple, J.C., Jie Zhang and ChunSheng Xiang. 1993. Chromosome numbers in Fam. Compositae, Tribe Astereae. V. Eastern North American taxa. Rhodora 95: 234-253.
Semple, J.C. 1995. A review of hypotheses on ancestral chromosomal base numbers in the tribe Astereae and the genus Aster. In D.J.N. Hind, C. Jeffrey and G.V. Pope, eds. Advances in Compositae Systematics. pp.153-165. Royal Botanic Gardens, Kew.
Xiang, ChunSheng and J.C. Semple. 1996. Molecular systematic study of Aster sensu lato and related genera (Asteraceae: Astereae) based on chloroplast DNA restriction site analyses and mainly North American taxa.. In D.J.N. Hind (Editor-in-Chief). Proceeding of the International Compositae Conference, Kew, 1994. Vol. 1. Systematics (vol. eds D.J.N. Hind and H. Beentje). pp. 393-423. Royal Botanic Gardens, Kew.
Semple, J.C., S. Heard and ChunSheng Xiang. 1996. The Asters of Ontario (Compositae: Astereae): Diplactis Raf., Oclemena Greene, Doellingeria Nees and Aster L. (including Canadanthus Nesom, Symphyotrichum Nees and Virgulus Raf.). U. Waterloo Biol. Series 38: 1-94.
Semple, J.C., ChunSheng Xiang, Jie Zhang, M. Horsburgh and R. Cook. 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.
ALLEN, G.A.*, BROUILLET, L., SEMPLE, J.C. 2001. A molecular phylogeny of the Eucephalus asters (Asteraceae) based on ITS sequences, with biogeographic and morphological inferences. CBA/ABC Meeting, Kelowna, BC, June 2001.
BROUILLET, L.*, ALLEN, G. , SEMPLE, J.C., and ITO, M. 2001. ITS phylogeny of North American asters (Asteraceae: Astereae): basal grade to North American lineages and distinct from Eurasian ones. 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). Botany 2001 [ASPT/BSA/IOPB joint meeting] Albuquerque, New Mexico 12-16 August 2001.
Chmielewski, J.G., and J.C. Semple. 2001. The Biology of Canadian weeds. 113. Symphyotrichum lanceolatum (Willd.) Nesom [Aster lanceolatus Willd.] and S. lateriflorum (L.) Löve & Löve [Aster lateriflorum (L.) Britt.]. Canad. J. Plant Sciences 81: 829-849.
Chmielewski, J.G., and J.C. Semple. 2001. The Biology of Canadian weeds. 114. Symphyotrichum pilosum (Willd.) Nesom (Aster pilosus Willd.). Canad. J. Plant Sciences 81: 851-865.
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., Doellingeria Nees, Oclemena E.L. Greene, Eurybia (Cass.) S.F. Gray, Canadanthus Nesom, and Symphyotrichum Nees (including Virgulus Raf.). U. Waterloo. Biol. Series No. 41: 1-134. [abstract]
Chmielewski, J.G., and J.C. Semple. 2003. The biology of Canadian weeds. 125. Symphyotrichum ericoides (L.) Nesom (Aster ericoides L.) and S. novae-angliae (L.) Nesom (A. novae-angliae L.). Canad. J. Plant Sciences 83: 1017-1037.
Semple, J.C., and R.E. Cook. 2004. Chromosome numbers in Fam. Compositae, Tribe Astereae. VII. Some eastern North American and Eurasian taxa. Rhodora 106: 253-272.
Semple, J.C. 2004. Miscellaneous nomenclatural changes in Astereae (Asteraceae). Sida 21(2): 759-765.
Leonard, M.R, R.E. Cook and J.C. Semple. 2005. A multivariate morphometric study of the aster genus Sericocarpus Nees (Asteraceae: Astereae). Sida 21: 1471-1505.
Semple, J.C. and J.L.A. Hood. 2005. Pappus variation in North American Asters. I. Double, triple and quadruple pappus in Symphyotrichum and related aster genera (Asteraceae: Astereae). Sida 21: 2141-2159.
Semple, J.C. and J. G. Chmielewski. 2006. Doellingeria Nees. pp. 43-46. In Flora North America Editorial Committee, eds. Flora of North America. Vol. 20. Asteraceae, Part. 2. Astereae and Senecioneae. Oxford University Press.
Semple, J.C. and M.R. Leonard. 2006. Sericocarpus Nees. pp. 101-105. In Flora North America Editorial Committee, eds. Flora of North America. Vol. 20. Asteraceae, Part 2. Astereae and Senecioneae. Oxford University Press, New York.
Semple, J.C. 2006. Ampelaster Nesom. pp. 460. In Flora North America Editorial Committee, eds. Flora of North America. Vol. 20. Asteraceae, Part 2. Astereae and Senecioneae. Oxford University Press.
Brouillet, L., J.C. Semple, G.A. Allen, K. Chambers and S. Sundberg. 2006. Symphyotrichum Nees pp. 465-539. In Flora North America Editorial Committee, eds. Flora of North America. Vol. 20. Asteraceae, Part 2. Astereae and Senecioneae. Oxford University Press.
Brouillet, L., T. Lowrey, L. Urbatsch, V. Karaman-Castro, G. Sancho, S. Wagstaff, and J.C. Semple. 2009. Chapter 37. Astereae. 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.
Chen, Y.L., Y.S. Chen, L. Brouillet and J.C. Semple. 2011. Astereae. Pp. 545–652 in: Wu, Z.Y., Raven, P.H. & Hong, D.Y., eds., Flora of China Volume 20–21 (Asteraceae). Science Press (Beijing) & Missouri Botanical Garden Press (St. Louis). Published online on 25 October 2011. Printed version December 2011.
Chen, Y.L., L. Brouillet and J.C. Semple. 2011. Aster Linnaeus. pp. 574-632. In Wu, Z.Y., Raven, P.H. & Hong, D.Y., eds., Flora of China Volume 20–21 (Asteraceae). Science Press (Beijing) & Missouri Botanical Garden Press (St. Louis). Published online on 25 October 2011. Printed version December 2011.
Semple, J.C. 2012. Almutaster p. 350-352. Sericocarpus p. 420. In B. G. Baldwin et al. (eds.), The Jepson Manual, Vascular Plants of California. 2nd Ed. University of California Press., Berkeley
Semple J.C., R.E. Cook, and E. Owen. 2015. Chromosome numbers in Fam. Compositae, Tribe Astereae. VIII. Eastern North American taxa. II. Rhodora 117: 80-91.
Semple, J.C., R.E. Cook, G.H. Morton, J.B. Beck, and R.M. Lopez Laphitz. 2019. Chromosome number determinations in Fam. Compositae, Tribe Astereae. IX. North American taxa. II. Rhodora 121: 37-53.
Semple, J.C. 2019. Symphyotrichum estesii (Astearaceae: Astereae), a new species of virguloid aster from Tennessee. Phytoneuron 2019-36: 1-10.
revised 16 October 2019 by J.C. Semple
© 2019 J.C. Semple, including all photographs unless otherwise indicated