Amsonia is a genus of perennial herbs in the dogbane family, Apocynaceae, order Gentianales, commonly known as bluestars. The genus was first described by Thomas Walter in 1788 and comprises around 17–20 species. Most species are native to North America, with the greatest diversity in the southeastern and southwestern United States and northern Mexico; one species (Amsonia elliptica) occurs in East Asia (China, Japan, and Korea), and one (Amsonia orientalis) grows in the eastern Mediterranean region of Greece and Turkey.
Plants are erect, clumping perennials that exude a milky latex when cut. Stems are typically unbranched to sparingly branched, bearing deciduous, alternate leaves. The flowers are the genus's most distinctive feature: small, star-shaped, and borne in terminal clusters, they are typically blue to purplish (sometimes white or lavender), with a narrow salverform corolla — the "blue stars" that give these plants their common name. Fruits are paired slender follicles, brown at maturity, containing cylindric or fusiform seeds.
Three subgenera are recognized within Amsonia: subg. Amsonia (southeastern and south-central United States), subg. Articularia (southwestern United States, distinguished by moniliform mature follicles), and subg. Sphinctosiphon (southwestern United States). The genus is taxonomically complex; several species, particularly in the southeastern United States, show high variability with no definitive boundaries.
Well-known members include Amsonia tabernaemontana (eastern bluestar), widely cultivated as an ornamental, and Amsonia hubrichtii (Hubricht's bluestar), valued for its brilliant golden fall foliage.
Etymology
The genus name Amsonia honors Dr. John Amson, an eighteenth-century physician in Williamsburg, Virginia, who served as the city's mayor in 1750 and 1751. The genus was formally described by Thomas Walter in 1788 in Flora Caroliniana. The common name "bluestars" refers to the characteristic star-shaped blue flowers.
Distribution
Amsonia is primarily a North American genus, with species distributed across the eastern, central, and southwestern United States and into northern Mexico. One species, Amsonia elliptica, occurs disjunctly in East Asia (China, Japan, Korea), and one, Amsonia orientalis, is native to the eastern Mediterranean (Greece and Turkey). The southwestern United States harbors the greatest species diversity, particularly in Arizona and New Mexico.
Taxonomy Notes
Amsonia was described by Thomas Walter in Flora Caroliniana (1788) and placed in the family Apocynaceae, order Gentianales. Three subgenera are currently recognized: subg. Amsonia (SE/SC United States, corolla tubes broadest at apex), subg. Articularia (SW United States, moniliform mature follicles), and subg. Sphinctosiphon (SW United States, terete follicles). The genus is taxonomically problematic; species in the southeastern and south-central United States are highly variable with persistent nomenclatural issues. The chromosome base number is x = 11.
