Spigelia is a genus of around 60 species of flowering plants in the family Loganiaceae, order Gentianales. It ranges across the warmer parts of the Americas, from northern Argentina and the latitude of Buenos Aires north through Central America to the southern United States. The genus was established by Carl Linnaeus in his landmark 1753 Species Plantarum, where he named it in honor of the Flemish-Italian botanist Adriaan van den Spiegel (Adrianus Spigelius, 1578–1625). The type species is Spigelia anthelmia.
Plants in the genus are herbaceous perennials or annuals. The most widely cultivated and studied species, Spigelia marilandica (Indian pink or woodland pinkroot), grows to about 50 cm tall with striking tubular flowers that are red on the outside and yellow within, attracting hummingbirds. It is native to the eastern and south-central United States, where it inhabits rich dry soils at woodland edges, and is hardy to approximately −15°C.
The genus is colloquially known as "pinkroot," reflecting both the color of the flowers and the historical use of the root as a medicinal anthelmintic by Native American peoples and later in colonial medicine. The roots contain the alkaloid spigiline, which expels intestinal worms but is toxic in excess, requiring careful dosing.
Etymology
The genus name Spigelia honors Adriaan van den Spiegel (Latinized as Adrianus Spigelius, 1578–1625), a Flemish-Italian anatomist and botanist. The name was given by Carl Linnaeus in Species Plantarum (1753), making it one of the original Linnaean genera. The common name "pinkroot" refers to both the flower color and the historically important medicinal root.
Distribution
Spigelia is distributed across the warmer parts of the Americas, from roughly the latitude of Buenos Aires (Argentina) northward through South America, Central America, and into the southern United States. The genus reaches its northern limit in states such as Virginia, Ohio, and Kansas. Most species diversity is concentrated in South America, particularly Brazil and neighboring countries.
Ecology
Spigelia marilandica and related North American species inhabit rich, dry to moist soils at the margins of deciduous woodlands. They grow in semi-shaded to partially sunny conditions and tolerate a range of soil textures from sandy to clay, at mildly acid to mildly alkaline pH. The tubular red-and-yellow flowers of S. marilandica are specialized for hummingbird pollination.
Cultural Uses
Species in this genus, particularly Spigelia marilandica, have a long history of use as anthelmintics (agents that expel intestinal parasites). The root contains the alkaloid spigiline and was used by Indigenous peoples of eastern North America and later adopted in colonial and 19th-century Western medicine to treat tapeworm and roundworm infestations. The effective and toxic doses are close, so the root is considered potentially dangerous — overdose can produce increased heart rate, vertigo, convulsions, and death — and its medicinal use is only appropriate under professional supervision.
Cultivation
Spigelia marilandica is the most commonly cultivated species, valued for its ornamental tubular red-and-yellow flowers and its attraction of hummingbirds. It succeeds in most fertile soils in semi-shade and tolerates full sun where soil stays reliably moist. Plants are hardy to approximately −15°C (USDA zone 6/7). Propagation is by seed (requiring 3 weeks of cold stratification, then germination in 1–3 months at 20°C), spring division, or basal cuttings taken in late spring.
