Symphyotrichum boreale

Symphyotrichum boreale is a perennial herbaceous species that reaches between 13 centimetres (5 inches) and 85 cm (2 ft 9 in) high. The leaves, stem, and overall plant form are slender, and it produces long rhizomes. The inflorescence consists of one to several composite flowers. The ray florets are white to pale purple, and the disc florets are cream or pale yellow, becoming purplish.[4] The leaves are simple, with alternate or basal arrangement.[5]

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  Stem and flower head
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  Flower head
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  Involucres, phyllaries, and bracts
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  Stems and leaves
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  Stem close-up

Botanical illustration of S. boreale

Symphyotrichum boreale was formerly included in the large genus Aster as Aster borealis. However, this broad circumscription of Aster is polyphyletic and the North American asters are now mostly classified in Symphyotrichum and several other genera.[6]

Hybrids between this species and Symphyotrichum puniceum have been recorded and are called Symphyotrichum × longulum.[4]

Possible holotype of Aster longulus, basionym of hybrid Symphyotrichum × longulum

Symphyotrichum boreale is native to northern North America from Alaska to Newfoundland, and south to Colorado and West Virginia. It is found in wet, calcareous habitats including fens, marshes, swamps and wet meadows.[4]

In addition to vegetative spread via rhizomes, dispersal is accomplished by wind-blown seed.

The roots are colonised by fungi including arbuscular mycorrhiza and dark septate endophytes. The sac fungus Erysiphe cichoracearum, which causes a powdery mildew, is also known from this species.[7]