Native to the southeastern United States, blue star (Amsonia tabernaemontana) is a herbaceous perennial member of the dogbane (Apocynaceae) family that is hardy in the Chicago area. Often found growing streamside in sandy or gravelly soils, blue star has pale blue flowers in summer, followed by golden-yellow fall color. This species of amsonia is the most widely grown at the Chicago Botanic Garden.

How can a native of the Southeast be hardy in Chicago? The answer lies in the distribution of temperate-zone plants at the height of the last Ice Age. With Chicago covered in ice, the temperate-zone plants native to North America were restricted to a small band just north of the Gulf of Mexico. Extending from the northern hills of Georgia, Alabama, Mississippi, and Arkansas, the range arced southwest through the Edwards Plateau of Texas and ended in the mountainous regions of northern Mexico. At their coldest, these areas experience winter temperatures similar to those of Minnesota. When the glaciers retreated, some of the plant species were not able to migrate north as quickly as the ice melted because many of the animals responsible for pollinating and transporting seeds or plant parts had become extinct.

Members of the genus Amsonia are commonly known as bluestars for the abundant small blue flowers borne in clusters at the stem tips in late spring or early summer. The foliage ranges from threadlike to willow-like and looks attractive throughout the growing season with the bonus of good-to-outstanding yellow to gold fall color. Species may vary in plant size from a ground cover sized 5 inches to an almost shrub sized 4 feet. Bluestars are considered easy-to-grow, long-lived perennials, tolerant of many soil types.

Most amsonia are native to North America, but a few of the 22 species hail from Europe or Asia. The Chicago Botanic Garden's collection includes more than 20 varieties and more than 3,5000 individual plants. A number of these varieties have been evaluated for their performance in our region; Plant Evaluation Notes can be found on the Garden's website. The genus was named for Dr. Charles Amson, an 18th-century American colonist.