smooth blue aster

Smooth aster is 20 to 70 centimeters (8 to 28 inches) tall. Its leaves are arranged alternately on the stems, and their shape varies among lanceolate, oblong-ovate, oblong-obovate, and ovate. 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).

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. The whole flowerhead measures 13 to 25 millimeters (1⁄2 to 1 in) across.

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

Symphyotrichum laeve varieties are native to Canada, the United States, and Coahuila (Mexico). The species is introduced in Québec and New Brunswick. Symphyotrichum laeve grows in fields, open woods, and along roadsides in rocky or dry soil and full sun.

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