Blooming period: July to September
  Synonyms: Symphyotrichum spathulatum (Lindl.) Nesom var. spathulatum

Aster: from the Greek aster, "a star," describing the radiate heads of the flowers (ref. genus Aster)  -aster: a Latin substantival suffix indicating inferiority or incomplete resemblance, often used in naming wild equivalents of cultivated plants (e.g. oleaster, "wild olive," from olea, "olive"

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Moist habitats, 4000'-10000', montane coniferous
  forest
Growth habitat code of A. occidentalis abbreviated as FB = Forb/herb; This is generalized by the following: Vascular plant without significant woody tissue above or at the ground. Forbs and herbs may be annual, biennial, or perennial but always lack significant thickening by secondary woody growth and have perennating buds borne at or below the ground surface. In PLANTS, graminoids are excluded but ferns, horsetails, lycopods, and whisk-ferns are included.
Applies to vascular plants only. Federal Geographic Data Committee (FGDC) definition includes graminoids, forbs, and ferns.

Vertebrate poisons: mammals   (to livestock via selenium poisoning fide as Aster occidentalis)