Symphyotrichum laeve

Smooth aster is 20 to 70 centimeters (8 to 28 inches) tall.[7] Its leaves are arranged alternately on the stems, and their shape varies among lanceolate, oblong-ovate, oblong-obovate, and ovate.[8] They measure from 3 to 20 centimeters (1 to 8 inches) long and from 1 to 2.5 cm (3⁄8 to 1 in) wide. They are usually hairless, and the leaf edges are entire or bluntly or sharply toothed (crenate or serrate), sometimes with smaller teeth (serrulate).[7]

The flower heads are arranged in clusters (panicles). Each flower head has 13 to 23 ray florets with pale to dark blue or purple petals (laminae), and 19 to 33 disc florets that start out yellow and eventually turn purplish-red.[7] The whole flowerhead measures 13 to 25 millimeters (1⁄2 to 1 in) across.[8]

The seeds are cypselae with pappi (bristles at their tips).[7] Like the hairs on dandelion seeds, the pappi allow the seeds to be spread by the wind.[8]

There are four varieties: Symphyotrichum laeve var. laeve, S. laeve var. geyeri (Geyer's aster[3]), S. laeve var. concinnum, and S. laeve var. purpuratum.[7]

Hybrids with this species and others of the genus have been reported, including three named as follows:[9]

• Symphyotrichum × gravesii between S. laeve var. laeve and S. dumosum;
• Symphyotrichum × versicolor between S. laeve var. laeve and S. novi-belgii var. novi-belgii; and,
• Symphyotrichum × woldenii between S. laeve var. laeve and S. praealtum, which instead may be between S. oolentangiense and S. praealtum.

• 
  Symphyotrichum × gravesii
• 
  Symphyotrichum × versicolor
• 
  Symphyotrichum × woldenii

Symphyotrichum laeve varieties are native to Canada, the United States,[2] and Coahuila (Mexico).[3] The species is introduced in Québec and New Brunswick.[4]

S. laeve grows in fields, open woods, and along roadsides[10] in rocky or dry soil and full sun.[11]

Symphyotrichum laeve blooms in late summer and early fall. It is pollinated by many native bees[10] and attracts butterflies.[11] It is a larval host for the pearl crescent butterfly (Phyciodes tharos).[12][8]

• Astereae Lab - University of Waterloo
• Ontario Wildflowers