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Wisconsin Plant of the Week

Aster oolentangiensis Riddell

Asteraceae (Aster or Sunflower Family)

October 14, 2002

Common Name:

Sky-blue aster, prairie heart-leaved aster

Sky-blue aster is a native perennial plant of sandy soils, dry to wet prairies and oak savannas throughout the tallgrass prairie region. Prairie heart-leaved aster may be a better common name since the ray flowers vary from blue through lavender to pale pink.

Whatever name you use, itís one of the last asters to bloom in the fall.  Flower heads are 2 to 3 cm across on erect reddish stems up to 1 m tall.  The disc flowers in the center of each head are yellow.  Plants bloom only after 2 or 3 growing seasons and spread slowly by seed and short rhizomes.

Lower leaves (inset) are thick and firm with a rounded or heart-shaped base, a smooth margin and a long, often red, petiole or leaf stalk. Both the upper and lower leaf surfaces are very rough.  Further up the stem the leaves become abruptly smaller, narrower and lack any leaf stalk. Where the plants form large patches, the absence of large leaves among the flowers makes for showy floral displays, especially against the drying prairie grasses.

Wisconsin has about 30 Aster species, many of which form hybrids. All have a similar flower structure and bloom after midsummer. Sky-blue aster is one of a subset of 7 Asters with long-stalked heart-shaped basal leaves.  The very firm rough leaves with smooth edges are distinctive.  Another key character is the phyllaries, or leafy bracts on the underside of each flower head.  These are 1 mm wide and very pale green with dark green diamond-shaped tips.

  • Origin of the name: Aster, Gk., star, for the shape of the flower head; oolentangiensis, for the Olentangy River in Ohio where the type specimen for the species was first collected. Formerly A. azureus.
  • Range:  Eastern N. Amer. Ontario, NY, OH, w. to SD, s. to TX, FL
  • WI Range:  common on sandy soil except in the Northern Highlands
  • Common associates: big bluestem, spiderwort, rough blazingstar
  • Wetland Indicator Status: [UPL]
  • Coefficient of Conservatism: 5, WI; 4, MI; 8, Chicago Region
     
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