Plant 98

Aster species (Asteraceae)


Michaelmas daisies

Michaelmas daisies are perennial, horticultural stars of the late summer and autumn but they are not a single species, or even a single genus. The current common name refers to the late flowering, around Michaelmas (29th September), whilst a former common name (starwort) and the scientific name refers to the shape of the flower heads.

European and North American Michaelmas daisies have been a feature of British gardens since the sixteenth century, and have been grown in the Oxford Botanic Garden since 1648. An early North American introduction was apparently made by John Tradescant the Younger. Generations of selection and hybridisation by horticulturalists, among Michaelmas daisies from across the globe, produced thousands of cultivars, a multi-million pound horticultural trade and complex patterns of relationships that are difficult to disentangle.

At the beginning of the twentieth century, the genus Aster contained more than 500 North American and Eurasian species. Since 1753, when the Swedish botanist Carolus Linnaeus first formally named the genus based on a European species, it had become a taxonomic 'dustbin'. Botanists placed morphologically similar species, that they could not readily be put into other genera, into Aster. This state of affairs changed in the 1990s when detailed scientific investigations of the morphology and DNA of species from across the geographic range of the genus were published. These studies showed North American members of the genus form a group that is evolutionary distinct from Eurasian species; scientific names had to change to reflect this new research.

Despite perceptions, botanists are reluctant to change scientific names, particularly for economically important plants, because of the confusion that may be caused. One reason generic names change is when new taxonomic research shows convincingly they comprise more than one thing; Aster is a case in point. The genus Aster was shorn of almost all of its North American members. The rules of naming plants mean the name Aster must refer to the Eurasian plants; today the genus comprises approximately 180 species. On-going research shows even the current concept of Aster may be too broad, and that additional pruning may be necessary to accommodate evolutionary relationships among Asian species. The North American Michaelmas daisies are now split among approximately a dozen genera.

The consequences of such research for botanists and horticulturalists who use scientific names have been profound, but most gardeners still use Michaelmas daisy and aster as if referring to the unshorn genus.

Further reading

Li W-P et al. 2012. Phylogenetic relationships and generic delimitation of Eurasian Aster (Asteraceae: Astereae) inferred from ITS, ETS and trnL-F sequence data. Annals of Botany 109: 1341-1357.

Noyes RD and Rieseberg LH 1999. ITS sequence data support a single origin for North American Astereae (Asteraceae) and reflect deep geographic divisions in Aster s.l. American Journal of Botany 86: 398-412.

Picton P and Picton H 2015. The plant lover's guide to asters. Timber Press.

Stephen Harris

The 25th July 2021 marks 400 years of botanical research and teaching by the University of Oxford.

As a celebration and count-down to this anniversary, the University of Oxford Botanic Garden and Harcourt Arboretum, together with the Oxford University Herbaria and the Department of Plant Sciences, will highlight 400 plants of scientific and cultural significance. One plant will be profiled weekly, and illustrated with images from Oxford University's living and preserved collections.

  • Plant 97: Hylocereus undatus
  • Plant 96: Cercidiphyllum japonicum
  • Plant 95: Nicotiana tabacum
  • Plant 94: Atropa belladonna
  • Plant 93: Solanum lycopersicum
  • Plant 92: Zea mays
  • Plant 91: Dionaea muscipula
  • Plant 90: Eryngium sp.
  • Plant 89: Mimosa pudica
  • Plant 88: Pinus nigra
  • Plant 87: Catharanthus roseus
  • Plant 86: Lantana camara
  • Plant 85: Stipa gigantea
  • Plant 84: Gunnera manicata
  • Plant 83: Rosa chinensis
  • Plant 82: Aconitum napellus
  • Plant 81: Pteridium aquilinum
  • Plant 80: Wisteria sinensis
  • Plant 79: Passiflora alata
  • Plant 78: Matteuccia struthiopteris
  • Plant 77: Acer carpinifolium
  • Plant 76: Vicia faba
  • Plant 75: Calycanthus floridus
  • Plant 74: Primula auricula
  • Plant 73: Strongylodon macrobotrys
  • Plant 72: Capsella bursa-pastoris
  • Plant 71: Barnadesia caryophylla
  • Plant 70: Erythronium dens-canis
  • Plant 69: Trifolium dubium
  • Plant 68: Forsythia spp.
  • Plant 67: Ananas comosus
  • Plant 66: Theobroma cacao
  • Plant 65: Nostoc sp.
  • Plant 64: Sciadopitys verticillata
  • Plant 63: Garrya elliptica
  • Plant 62: Psilotum nudum
  • Plant 61: Cyclamen species
  • Plant 60: Hevea brasiliensis
  • Plant 59: Semele androgyna
  • Plant 58: Monstera deliciosa
  • Plant 57: Musa textilis
  • Plant 56: Piper nigrum
  • Plant 55: Viscum album
  • Plant 54: Dieffenbachia seguine
  • Plant 53: Salvinia molesta
  • Plant 52: Saccharum officinarum
  • Plant 51: Metasequoia glyptostroboides
  • Plant 50: Equisetum sp.
  • Plant 49: Fraxinus excelsior
  • Plant 48: Rosmarinus officinalis
  • Plant 47: Ptelea trifoliata
  • Plant 46: Acer saccharum
  • Plant 45: Brassica oleracea
  • Plant 44: Helianthus annuus
  • Plant 43: Ricinus communis
  • Plant 42: Simmondsia chinensis
  • Plant 41: Chara sp.
  • Plant 40: Zingiber officinale
  • Plant 39: Aristolochia clematitis
  • Plant 38: Allium cepa
  • Plant 37: Galium tricornutum
  • Plant 36: Artemisia annua
  • Plant 35: Rosa canina
  • Plant 34: Nepenthes rajah
  • Plant 33: D. caryophyllus x barbatus
  • Plant 32: Taraxacum sp.
  • Plant 31: Victoria cruziana
  • Plant 30: Lathyrus odoratus
  • Plant 29: Heliconia rostrata
  • Plant 28: Senecio squalidus
  • Plant 27: Paulownia tomentosa
  • Plant 26: Urtica dioica
  • Plant 25: Euphorbia characias
  • Plant 24: Heliamphora nutans
  • Plant 23: Laurus nobilis
  • Plant 22: Tulipa sylvestris
  • Plant 21: Pleurococcus sp.
  • Plant 20: Gleditsia triacanthos
  • Plant 19: Tillandsia usneoides
  • Plant 18: Marchantia polymorpha
  • Plant 17: Daphne mezereum
  • Plant 16: Citrus medica
  • Plant 15: Coffea arabica
  • Plant 14: Gossypium species
  • Plant 13: Stachyurus praecox
  • Plant 12: Encephalartos ferox
  • Plant 11: Aloe vera
  • Plant 10: Araucaria angustifolia
  • Plant 9: Isoetes echinospora
  • Plant 8: Hamamelis virginiana
  • Plant 7: Lithops species
  • Plant 6: Sequoiadendron giganteum
  • Plant 5: Commiphora saxicola
  • Plant 4: Buxus sempervirens
  • Plant 3: Picea abies
  • Plant 2: Cinnamomum verum
  • Plant 1: Taxus baccata

  • Follow us on Twitter @Plants400

    The data and images available on this site may only be used for scientific purposes. They may not be sold or used for commercial purposes. All images are copyright of the University of Oxford, unless otherwise indicated.

    The specimens at the Oxford herbaria and the living collections of the Oxford Botanic Garden and Oxford University Herbaria are being digitized using BRAHMS.


    Dr Stephen Harris (